The use of exhaust gas recirculation (EGR) is necessary to improve the thermal efficiency of spark-ignition engines. However, deposits formed in the EGR valve or cooler cause valve sticking and reduced heat exchange performance of the cooler, which are serious problems. In this study, the formation mechanism of EGR deposits was investigated using the gasoline engine exhaust and an EGR deposit model was constructed. As a result, it was found that the deposit was formed under the conditions where the wall temperature was below 200 ℃, and the amount of the deposit increased with decreasing the wall temperature between 80 and 200 ℃. The developed model predicted the experimental results well.