In recent years, automobile engines are required to have higher performance, higher output and a better fuel economy. In engine development to respond to this, especially in the development of downsizing turbo engines, it is important to suppress the wear of the valve seat on the exhaust side caused by high temperature and high load. In order to shorten the development period, it is required to estimate the amount of wear of the valve seat before the actual engine test at the design stage of development. The objective of this research was to predict the amount of the wear of the valve seat on the exhaust side of gasoline engine durability test based on the results of unit test. In the unit test, the wear rate was measured for some cases when the factors of valve seat wear were within a certain range. The wear amount calculation formula was constructed using the results for factors that were especially sensitive. The amount of wear calculated from the wear amount formula and the driving mode of the actual engine showed a strong correlation with the wear amount of the bench durability test and the wear amount of the road test. The results also showed that even when the valve seat material and valve diameter are different, the amount ware in actual engine scan still be similarly estimated by devising a wear formula.