This study is concerned with the prediction of warranty period for ignition coil. Generally, first of all, reliability test items are determined by analysing design FMEA(Failure Mode Effect Analysis), process FMEA, and fault mode data. Then, production reliability acceptance test is performed, including vibration test, salt fog test, thermal shock test, and temperature cycle test. This study was focused on the problems which can occur when warranty period extension is assumed by the result of production reliability acceptance test. Assuming these cases, a variety of analysis was performed, using standard probability, conditional probability, failure rate, warranty(time) information, B life and mean life of ignition coil. As a result, reliable warranty periods were determined and failure causes were found by in this method.