Thailand is an agriculture-based country with the potential to cultivate a vast array of plant species, including castor. Castor oil is produced by pressing castor seeds. Castor oil was selected as the preferred vegetable oil for biodiesel production. Castor oil is primarily composed of ricinoleic acid, a hydroxyl fatty acid. Response surface methodology was used in this study to optimize the biodiesel production process parameters. This study varies the molar ratio of methanol to oil, the concentration of the catalyst, the reaction temperature, and the reaction time. As a catalyst, potassium hydroxide was used in the transesterification process. In this study, response surface methodology is utilized in conjunction with central composite design (CCD) experiment design. Therefore, the optimal yield of castor oil transesterification is 4.02 methanol to 1 oil, a catalyst concentration of 0.90%, a reaction temperature of 49.87 ∘C, and a reaction time of 59.21 minutes. These optimal conditions resulted in a %fatty acid methyl ester (FAME) yield of castor oil biodiesel of 88.25 %, which is within 5% of the predicted %FAME yield. Transesterification under optimal conditions demonstrates that the physiochemical properties of castor oil biodiesel are enhanced. The viscosity of castor oil is approximately 235 cSt at 40 ∘C. After transesterification, the viscosity of castor oil decreases to 15.2 cSt at 40 ∘C under optimal conditions. The density and flash point of castor oil biodiesel is 0.92 g/cm3 and 196 ∘C, respectively. It discovers that the flash point of castor-oil biodiesel complies with the American Society for Testing and Materials (ASTM) standard, whereas its viscosity and density do not. However, castor oil biodiesel can be blended with diesel petroleum to reduce its viscosity and meet ASTM specifications.