PURPOSE: To monitor the coating characteristics of an optical fiber nondestructively and continuously by providing an induction coil for receiving a coated optical fiber, and means for designating the induction colt to measure an electric value corresponding to specific characteristics of the coating.

CONSTITUTION: An induction coil 24 is connected with a Q meter 26 through a lead 34 and the coil 24 is surrounded by an electric interference shield 28. The means 26 comprises a meter 36 indicating an electric value Q measured in response to activation of the coil 24. The induction coil 24 is activated prior to monitoring and adjusted to tune under unloaded state. Monitoring is then performed while activating the coil 24 with a frequency providing a highest Q at the time of tuning. According to the method, the coating characteristics of an optical fiber can be monitored nondestructively and continuously.