In this study, organic compounds of Mn, Mg, Cu and Ca metals were synthesized., and their solutions were used as Diesel fuel additives. The additives that achieved the greatest decrease in freezing point of Diesel fuel. its optimum rate of dosage and other performance effects were tested. The results showed that the organic based manganese gave the greatest decrease in freezing point. This additive reduced the freezing point to 12.4degreesC at the rate of dosage of 54.2 mumol Mn/l Diesel fuel. It was established that the cetane number of Diesel fuel without the additive was 46.22, whereas the cetane number was 48.24 for Diesel fuel with the optimum amount of dosage. It was observed that the organic based manganese drops the viscosity and flash point and improves the contents of the exhaust gases. (C) 2002 Elsevier Science Ltd. All rights reserved.