Biodiesel is an alternative diesel engine fuel. It should commonly be used as it is environmentalist and renewable. There are, of course, same doubts about its usage. The most important doubt is whether the utilization of biodiesel damages the engine or not. In this article, the research results obtained on biodiesel usage on an engine are presented. The cases that have to be taken care of by the biodiesel users and the effects of biodiesel used as fuel were determined. The present work has been realized to consider the influences of biodiesel on engine fuel system parts and engine components at real time and long-term conditons.