Increase of environmental problems and depletion of fossil fuels are the driving forces to promote biodiesel as an alternative fuel in diesel engines. In the present work, biodiesel was prepared by transesterification of waste cooking oil with methanol and its physical and chemical properties were measured and found to be within acceptable limits of standard specifications of regular diesel fuel. Performance and emissions characteristics of a diesel engine running using biodiesel (B100) and its blends with kerosene were then assessed and compared to those using regular diesel (D100). Two biodiesel blends of biodiesel with kerosene have been used in this study containing 25 and 50% by volume kerosene as (K25) and (K50), respectively. The used engine was a direct injection four stroke, four cylinders diesel engine and it was run at two engine speeds being 1250 rpm and 900 rpm. The results have shown that the composition of the exhaust gases of the engine running at both speeds was better using biodiesel instead of regular diesel and it has been improved further by blending biodiesel with kerosene. With respect to the brake thermal efficiency, it was found that the use of biodiesel instead of regular diesel reduced the thermal efficiency at 1250 rpm while the reverse was true at a lower running speed of 900 rpm. However at both engine speeds, the thermal efficiency can be improved by blending biodiesel with kerosene.