Biodiesel is a kind of clean and renewable energy which can be used directly or mixed with fossil diesel as fuel on vehicles. It can be extracted from recycled vegetable oil or animal fat by using blending, diluting, microemulsion, pyrolysis, or transesterification method. Transesterification means that appropriate amount of alcohols and fat are mixed in supercritical condition with various kind of catalyst to produce esters. It is a common process in producing biodiesel. By using all kinds of catalyst, heterogeneous catalyst is relatively environment-friendly and makes a simple process. In this study, soy bean oil is mixed with methanol under 60℃ with sodium hydroxide as catalyst to investigate the effect of molar ratio between oil and methanol and catalyst amount. Hydrotalcite, one kind of homogeneous catalyst, is then produced at different temperature by 3:1 Al/Mg molar ratio after the best ratio between oil and methanol is determined. Sodium hydroxide is then replaced by hydrotalcite to examine the performance of hydrotalcite as catalyst. As result, the best ratio between oil and methanol is 6:1 with Sodium hydroxide as catalyst. Conversion ratio and reaction rate are both improved with increasing catalyst amount. In preparation of hydrotalcite, crystallization dimension is reduced at higher calcination temperature which makes a larger accessible area. The content of Alumium oxide is decreasing with increasing magnesium oxude. Alumium oxide is all replaced by MgAl2O4 when calcination temperature is rised to 650℃. Hydrotalcite made at 550℃ has the best result in conversion ratio and conversion ratio does not rise significantly with increasing catalyst amount in long term reaction time. However, the initial reaction rate is clearly related to the catalyst amount.