diff --git a/agent/config.py b/agent/config.py
index 8be8dcb..a4a12dd 100644
--- a/agent/config.py
+++ b/agent/config.py
@@ -62,4 +62,7 @@ class Settings(BaseSettings):
     DAILY_COST_LIMIT_USD: float = 10.0
     PER_TASK_COST_LIMIT_USD: float = 3.0
 
+    # Logging
+    LOG_FORMAT: str = "json"
+
     model_config = {"env_file": ".env", "extra": "ignore"}
diff --git a/agent/json_logging.py b/agent/json_logging.py
new file mode 100644
index 0000000..69adc76
--- /dev/null
+++ b/agent/json_logging.py
@@ -0,0 +1,55 @@
+"""구조화 JSON 로깅.
+
+LOG_FORMAT 환경변수로 json | text 선택 가능.
+"""
+from __future__ import annotations
+
+import json
+import logging
+import traceback
+from datetime import datetime, timezone
+
+_BUILTIN_ATTRS = {
+    "args", "created", "exc_info", "exc_text", "filename", "funcName",
+    "levelname", "levelno", "lineno", "module", "msecs", "message", "msg",
+    "name", "pathname", "process", "processName", "relativeCreated",
+    "stack_info", "thread", "threadName", "taskName",
+}
+
+
+class JsonFormatter(logging.Formatter):
+    def format(self, record: logging.LogRecord) -> str:
+        log_data = {
+            "timestamp": datetime.fromtimestamp(record.created, tz=timezone.utc).isoformat(),
+            "level": record.levelname,
+            "logger": record.name,
+            "message": record.getMessage(),
+        }
+        for key, value in record.__dict__.items():
+            if key not in _BUILTIN_ATTRS and not key.startswith("_"):
+                try:
+                    json.dumps(value)
+                    log_data[key] = value
+                except (TypeError, ValueError):
+                    log_data[key] = str(value)
+        if record.exc_info and record.exc_info[0] is not None:
+            log_data["exception"] = "".join(traceback.format_exception(*record.exc_info))
+        return json.dumps(log_data, ensure_ascii=False)
+
+
+def setup_logging(
+    log_format: str = "json",
+    level: int = logging.INFO,
+    logger: logging.Logger | None = None,
+) -> None:
+    target = logger or logging.getLogger()
+    if log_format == "json":
+        formatter = JsonFormatter()
+    else:
+        formatter = logging.Formatter(
+            "%(asctime)s %(levelname)s %(name)s: %(message)s",
+            datefmt="%Y-%m-%dT%H:%M:%S",
+        )
+    for handler in target.handlers:
+        handler.setFormatter(formatter)
+    target.setLevel(level)
diff --git a/tests/test_json_logging.py b/tests/test_json_logging.py
new file mode 100644
index 0000000..5ddfaa3
--- /dev/null
+++ b/tests/test_json_logging.py
@@ -0,0 +1,80 @@
+import json
+import logging
+import io
+
+from agent.json_logging import JsonFormatter, setup_logging
+
+
+def test_json_formatter_basic():
+    formatter = JsonFormatter()
+    record = logging.LogRecord(
+        name="test", level=logging.INFO, pathname="test.py",
+        lineno=1, msg="테스트 메시지", args=(), exc_info=None,
+    )
+    output = formatter.format(record)
+    parsed = json.loads(output)
+    assert parsed["message"] == "테스트 메시지"
+    assert parsed["level"] == "INFO"
+    assert "timestamp" in parsed
+
+
+def test_json_formatter_with_extra():
+    formatter = JsonFormatter()
+    record = logging.LogRecord(
+        name="test", level=logging.INFO, pathname="test.py",
+        lineno=1, msg="작업 시작", args=(), exc_info=None,
+    )
+    record.thread_id = "uuid-123"
+    record.issue = 42
+    output = formatter.format(record)
+    parsed = json.loads(output)
+    assert parsed["thread_id"] == "uuid-123"
+    assert parsed["issue"] == 42
+
+
+def test_json_formatter_with_exception():
+    formatter = JsonFormatter()
+    try:
+        raise ValueError("test error")
+    except ValueError:
+        import sys
+        record = logging.LogRecord(
+            name="test", level=logging.ERROR, pathname="test.py",
+            lineno=1, msg="에러 발생", args=(), exc_info=sys.exc_info(),
+        )
+    output = formatter.format(record)
+    parsed = json.loads(output)
+    assert "exception" in parsed
+    assert "ValueError" in parsed["exception"]
+
+
+def test_setup_logging_json():
+    test_logger = logging.getLogger("test_json_setup")
+    test_logger.handlers.clear()
+    test_logger.setLevel(logging.DEBUG)
+    stream = io.StringIO()
+    handler = logging.StreamHandler(stream)
+    test_logger.addHandler(handler)
+    setup_logging(log_format="json", logger=test_logger)
+    test_logger.info("hello")
+    output = stream.getvalue().strip()
+    parsed = json.loads(output)
+    assert parsed["message"] == "hello"
+
+
+def test_setup_logging_text():
+    test_logger = logging.getLogger("test_text_setup")
+    test_logger.handlers.clear()
+    test_logger.setLevel(logging.DEBUG)
+    stream = io.StringIO()
+    handler = logging.StreamHandler(stream)
+    test_logger.addHandler(handler)
+    setup_logging(log_format="text", logger=test_logger)
+    test_logger.info("hello")
+    output = stream.getvalue().strip()
+    assert "hello" in output
+    try:
+        json.loads(output)
+        assert False, "Should not be valid JSON"
+    except json.JSONDecodeError:
+        pass