This study was done to create and evaluate a compression tester adaptor for gasoline engines using a compression tester for diesel engines. It was conducted through an experimental study design. The null hypothesis of this study asserts that there is no significant difference in the mean compression of gasoline engines measured with a gasoline compression tester and gasoline engines measured with a diesel compression tester. Compression tester adapter was rejected because there was no significant difference in overall mean compression between gasoline engines tested with a gasoline compression tester and the same engines tested with a diesel compression tester equipped with a compression tester adapter in all number of tests. To save money, rather than purchasing another compression tester for gasoline engines, a compression tester adapter for gasoline engines was developed. This adapter was attached to the flexible hose of a diesel compression tester and fitted to the plug fitting of a gasoline engine to measure the engine's compression.