In this study, some physical properties of biodiesel obtained from different mixtures of sunflower oil and beef tallow are investigated. The biodiesel cold-flow specifications, such as viscosity, pour point, cloud point, and cold-filter plugging point, were tested for the different sunflower oil/beef tallow (SO/BT) ratios. Also, the sulfur content and heat value of the biodiesel samples have been determined. It was observed that the examined physical properties of the methyl esters changed negatively as the beef tallow ratio in the mixture increased. However, until the ratio of 40% beef tallow and 60% sunflower oil, there was no important deterioration in the properties of methyl esters. When beef tallow contents were higher than 40%, some specifications of methyl esters were beyond the biodiesel standards of ASTM D 6751 and EN 1424.