The effects of diesel fuel properties (aromatic content, cetane index and T90), cetane improver, oxygenates, high boiling point hydrocarbons and aromatics distribution on diesel exhaust emissions were studied under the Japanese 10-15 test cycle and the ECE+EUDC test cycle. The test vehicle was a TOYOTA COROLLA with a natural aspirated, 2.0L displacement, IDI diesel engine.It was demonstrated that particulate emissions are highly correlated with T90 and that NOx is affected by the aromatic content of fuel. A reduction in particulates emissions was observed in fuel with a lower cetane number by adding cetane improver, but this reduction was limited. Cetane improver had no effect on NOx emissions in the 45 # 60 cetane number range. Oxygenates reduced particulate emissions remarkably but had little effect on NOx emissions. A decrease in the soot in particulates was particularly observed. Particulate emissions seemed to be more affected by the blended oxygen content of oxygenated fuel than by its molecular structure, cetane number or boiling point. The reduction in particulates with oxygenated fuels was larger under the ECE+EUDC test cycle than the Japanese 10-15 test cycle. Di- and Triaromatics affected PM emissions more than Paraffin or Mono-aromatics.Furthermore, the effects of our test fuels were evaluated using a DI Diesel engine. Fuel with lower T90 and lower aromatic content reduced PM by 40% in the Japanese diesel 13 mode test. Cetane improver reduced ignition delay effectively, but had no effect on PM or NOx. Oxygenated fuel reduced PM emissions, however oxygenated fuel with a low cetane number increased PM given a specific injection timing under a high load condition.