Among several alternative for conventional automotive fuels, bio fuel is catching lot of attention due to its availability and emission characteristics. This review paper discussed about the comparative engine performance and emission characteristics of bio fuel and conventional fuel assist by several researchers. The bio fuel used in the form of various bio fuel such as ethanol, Jatropha, Mahua oil, Biodiesel,__ampersandsignnbsp;pongamia pinnata methyl ester (PPME), vegetable oil. Several bio fuel used as bio diesel.