Biodiesel represents a closed carbon dioxide cycle (approximately 78%) because it is derived from renewable biomass sources. "Bio" means its biological and renewable source, and "diesel" represents its use as a fuel on diesel engines. Biodiesel is defined as “mono-alkyl esters of long chain fatty acids derived from vegetable oils and animal fats". The present study was carried out in order to identify an effective treatment of used cooking oil to get the ideal specification condition to obtain high yield of biodiesel and get the best conversion ratio of used cooking oil to biodiesel. The linear regression analysis concluded that methanol to oil ratio and catalyst concentration have a high positive statistical significant effect. Temperature has a positive statistical significant effect. The process time had a non statistical significant negative effect on the biodiesel yield and the mixing rate had a highly negative statistical significant effect. The best methyl ester conversion obtained was 99.2 wt.% based on the following conditions : methanol to oil molar ratio of 7.54:1, catalyst concentration of 0.875% , 1.17 hr. of reaction time, temperature of 52 °C, mixing rate 266 rpm.