Alumina-supported potassium oxides are promising catalysts for the transesterification reaction of vegetable oils for biodiesel production. Various potassium compounds Al2O3-supported were prepared via impregnation method. Potassium oxide (K2O) is a good candidate for a solid base catalyst from an economical point of view. In the present work, we reviewed K2O catalyst for the vegetable oil transesterification based on a variety of related research papers. The potassium compounds supported in catalysts, KOH/Al2O3, KNO3/Al2O3, KI/Al2O3, KF/Al2O3 and K2CO3/Al2O3, were optimized through various reaction parameters, such as: amount of catalyst, molar ratio of oil to alcohol, reaction time and temperature. Yields and conversions from various catalytic systems applied for biodiesel production were also compared. Among the catalysts studied, the KF/Al2O3 showed higher catalytic activity and a small amount of catalyst requirement in the transesterification reaction, indicating that it can be applied as a potential catalyst in the industry.