Extension on overhaul inspection period of the main bearing of main diesel engine is highly desired by carrying out its condition monitoring. The effective condition monitoring method is required instead of the temperature method which rises out the warning alarm after bearings appeared in critical condition. It was found also for plane bearing that the contact between the shaft and bearing may occur locally even in the oil film lubrication state. Result from this study, the high frequency vibration measurement and wear particle detection in lubrication oil were suggested to be the effective condition monitoring methods.