This research was aimed to study producing biodiesel from used cooking oil with the transesterification reaction, As calcium oxide source via heterogeneous catalysts derived from Spotted Babylon. Using a potassium hydroxide impregnated on calcium oxide support catalysts. To reduce the use of potassium hydroxide and the optimal conditions for producing biodiesel. A series of experiments was conducted in order to evaluate the effects of reaction variables such as catalyst concentration (1-3%wt), molar ratio of methanol to oil (6:1 and 9:1) and under the terms of the retention time 2 h, temperature 65°C, and stirring intensity 250 rpm. The results showed that potassium hydroxide impregnated on calcium oxide support catalysts concentration 1%wt, molar ratio of methanol to oil 6:1. Result the most yield of biodiesel was 89.76%