This work focuses on production of biodiesel from natural and refined castor seed oil. Oil was extracted with normal-hexane solvent at 60°C using Soxhlet apparatus and pretreated by alkaline refining process before transesterification with methanolic potassium hydroxide solution as catalyst. The effect of alkaline refining on the oil characteristics and biodiesel quality parameters was investigated using standard test methods and fatty acid methyl ester was characterized using gas chromatography. Results revealed that alkaline refining had significant improvement on the oil and biodiesel characteristics. Yield of 43.9 and 46.2% were obtained for refined and unrefined castor oil respectively while biodiesel yield from refined and unrefined castor oil was 43.5 and 41.7% respectively. Ricinoleic acid (84.9%) was prevalent in the oil with lignoceric (0.03%) as the smallest. The conformity of refined castor oil biodiesel with EN 14214, ASTM and India biodiesel standards makes it viable economically in Nigeria.