Biodiesel is now well known as the alternative fuel for air pollution reduction from internal combustion engines using diesel fuel.Because of its oxygen components,particulates into the exhaust gas decrease dominantly and the thermal Nox increase.On the side of the improvement of the automobile performances,a lot of studies concerned with biodiesel are carried out widely.This study is objected to obtain the fundamental data related to the use of biodiesel on the home size boiler for the purpose of the heat efficiency increase and the decrease of the particulates.In this study,the mixing rate of biodiesel with kerosene using as the main fuel on the home size boiler is selected as the variables for finding out the mixing rate and summary of major results usable without any modification of the burner injection system.The spray characteristics on the pressure swirl nozzle which is generally used on the home size boiler burner with the biodiesel mixing rate are presented.Spray angle and mean drop size were measured by shadow graphic method and laser diffraction spectroscope.