To study the effect factors of biodiesel synthesis from vernicia montana oil using transesterification reaction. The series of experiment were carried out by using potassium hydroxide with 0.15, 0.35,0.55, 0.75, 0.95 and 1.50 wt% potassium hydroxide to vernicia montana oil between 10, 30, 60 and 90 minutes and vernicia montana oil to methanol molar ratio 1:3, 1:6, 1:9 and 1:12 in addition studied the effect of stirring speed at 200, 400, 600 round per minute. The experiment result showed that potassium hydroxide 0.95 wt% is suitable for the reaction. From the experiments at 600 rpm found that the maximum methyl ester contents obtained from the reaction at 50°C, 60 minutes were 96.7%. The obtained biodiesel from vernicia montana oil contained high values of iodine value and kinematic viscosity 40°C are 159.5 g I2/100 g and 8.22 mm2/s, respectively. Which are higher than the limit recommended biodiesel standard CNS 15072 and EN 14214 specification with iodine value lower than 120 g I2/100 g and kinematic viscosity 40 oC during 3.5–5.0 sq.mm./s, respectively. The vernicia montana oil may be not suitable for biodiesel product unless iodine value and kinematic viscosity 40°C are reduced.