Abstract: Steam generator secondary side foreign object may cause heat exchange tube wear which might threaten the integrity of steam generator tubes. A brief description was given on in-service inspection requirements for foreign objects. During the in-service eddy current inspection of steam generator tubes, an outer wall signal was found. Through BOBBIN probe and MRPC probe data analysis combined with secondary side video inspection, the tube outside wear caused by foreign objects was confirmed. Suggestions on monitoring the signal in the following in-service inspections were given.