Synthesis of biodiesel from waste cooking oil (WCO) using calcium oxide as heterogeneous catalyst which focusing on the effect of stirring speed was investigated. WCO can be utilized as biodiesel's raw material to reduce both biodiesel production as well as waste treatment cost. As WCO contained of solid and other impurities that need to be separated, a series of pre-treatment processes were applied. Subsequently, esterification process was done to decrease free fatty acid (FFA) content of WCO. As WCO contained low FFA content, trans-esterification was conducted to produce methyl ester. Transesterification process used CaO as heterogeneous base catalyst, so stirring speed is the important factor to produce high quality biodiesel. In this study, the effect of stirring speed on transesterification process using CaO were investigated in different stirring speeds for 4 hours with temperature of 60°C and loading catalyst CaO 1 wt% constantly. Biodiesel was characterized by FTIR, GC-FID, viscometer, pycnometer, and GC-MS. The yield and maximum methyl ester content were approximately 80% and 98.9%, respectively, under optimal operating stirring speed of 500 rpm. Biodiesel produced has already meet the specification in accordance to Indonesia Standard National (SNI) Biodiesel number 7182:2015.