Biodiesel can be used to reduce the emission pollution from diesel engines. The improvement of fuel properties through the use of (1% by wt) ozonated vegetable oil for neat biodiesel was evaluated. The pour point of biodiesel prepared from methanol transesterification of sunflower oil, linseed oil, and a mixed oil (from soy bean, sunflower and oleen oils) was dispersed to 0, -3, and 0 respectively. The cloud point remained unaffected except in the case of mixed oil biodiesel where a slight increase was observed. Ozonated mixed oil showed a decrease of flash point of corresponding biodiesel when the ozonated sample was prepared with sunflower ozoned oil. The tests of biodiesel degradation stored at different temperatures were monitored at regular intervals over a period of several weeks. Experimental results demonstrated that biodiesel showed an increase in acid value and decrease in viscosity nearly 10%, 5% and 2% within 8 weeks for those samples stored at room temperature 25-27 degrees C, at 4 degrees C and at -18 degrees C respectively. The same average decrease of viscosity (2%) was obtained for biodiesel samples ozonated and stored at room temperature 25-27 degrees C and those unozonated and stored at -18 degrees C, especially those produced from mixed oil. Microscopic analysis at low temperature revealed that ozonated mixed oil impeded agglomeration of biodiesel into a solidified material, giving crystals.