Exhaust odor of DI diesel engines is worse than that of gasoline engines, especially at low temperatures and at idling. As the number of passenger cars with DI diesel engines is increasing worldwide because of their low CO2 emissions, odor reduction research of DI diesel engines is important.Incomplete combustion is a major cause of exhaust odor. Generally, odor worsens due to overleaning of the mixture in the cylinder and due to fuel adhering on the combustion chamber walls. To confirm this, the influences of different engine running conditions and fuel properties were investigated. The reason for the changes in exhaust odor with injection timing is evaluated by considerations of optimum positions of the maximum heat release. With n-heptane, a low boiling point fuel, odorous emissions increase because of overleaning of the mixture. With 50% and 100% n-decane exhaust odor is significantly reduced due to optimum mixing of fuel with air, as well as because there is less adhering fuel and as n-decane has good ignitability. Overleaning of the mixture and fuel adhering to the walls were confirmed to be major factors influencing odorant formation in the cylinder.