To obtain the subject composition comprising dimethyl carbonate, acetaldehyde and ethyl nitrate and enabling to give a diesel fuel capable of reducing the contents of non-burnt substances on the combustion of the fuel in a diesel engine and further capable of reducing the contents of nitrogen oxides and carbon monoxide in an exhaust gas.

This additive composition for a diesel fuel comprises (A) dimethyl carbonate, (B) acetaldehyde and (C) ethyl nitrate. The components A, B and C are contained in amounts of 50-75vol.%, preferably 6-70vol.%, 25-40vol.%, preferably 30-35vol.%, and 10-15vol.%, preferably 12-13vol.%, respectively. The composition can be added in an amount of 3.5-5.5vol.%, preferably 4-5vol.%, to the diesel fuel to exhibit the effect.