This report deals with experiments carried out to examine the possibility of using unrefined rapeseed oil as a substitute for light oil in a small diesel engine. The authors carried out tests on short-term performance, long-term operation and no-load continuous operation using various kinds of unrefined rapeseed oil (deacidified oil, degummed oil and crude oil) produced in the process of refining, and refined rapeseed oil and light oil for comparison. Specific fuel consumption, thermal efficiency, exhaust-gas temperature, and density of black smoke in exhaust-gas were examined in tests on short-term performance and long-term operation. The amount of deposits in the precombustion chamber and on the injection nozzle was determined in tests on no-load continuous operation. As a result, it was considered that deacidified rapeseed oil can be used as fuel for a diesel engine. Degummed oil and crude rapeseed oil were found to be unsuitable for use as fuel due to the high level of incombustible materials in oil.