In SI engines with port injection system, fuel behavior both in the intake port and in the cylinder has significant influence on the transient A/F characteristics and HC emissions . Therefore, to improve the engine performance, it is very important to understand fuel behavior in the intake port and in the cylinder [2, 3].This paper describes the following three unique methods to analyze fuel behavior in port injected SI engines and some test results. (1)Observation of fuel behavior in the intake port, using a transparent intake air tube and a strobe synchronized TV-photographic system. (2)Observation of fuel behavior in the cylinder, using a glass cylinder and fluorescent fuel. (3)Measurement of fuel wall wetting in the intake port and in the cylinder, using the engine with electronically controlled hydraulically driven in-take/exhaust valves. With these three methods, it becomes possible to understand qualitatively and quantitatively the fuel behavior such as spray formation in the intake port, port wall wetting and cylinder wall wetting in firing operation.