The increase of population growth and development, as well as the area development by years affect the needs of electricity and fuel nationally. The case that crude oil or fossil fuel is a non-renewable resource, the bio-diesel, a renewable alternative as well as environmentally friendly fuel is highly needed. This research is aimed at optimizing the independent variable plan to produce the bio-diesel. In this research, the waste cooking oil was processed using transesterification method. To get the optimum bio-diesel, significant variables such as temperature and time needs to be optimized. The variation of each variable is gained from the data processing using Software Mini-tab 18 with Response Surface Method. It is revealed that the upper and lower range values of temperature are 45°C, 52.5°C and 60°C. Meanwhile, that of time are 30 minutes, 60 minutes, and 90 minutes. Based on the regression analysis and ANOVA, it is gained R-sq = 80.86% and p-value < 0.05. The optimum condition of the process is at 53.33°C and 60.30 minutes. The highest Yield of bio-diesel is 38.18%.