Palm stearin oil, which has a high melting point and Is generally used as the commercial raw material in oil chemistries, was hydrolyzed by a thermostable lipase produced from Pseudomonas sp, The initial reaction rate of oil hydrolysis was controlled by the interfacial area of the water/oil emulsion (W/O emulsion) where water was emulsified in oil, and it was represented by the Michaelis-Menten equation in which the interfacial area was substituted for the substrate concentration. A new bioreactor of a draft tube type which has the capability of functioning as an efficient continuous reactor for the separation of oil and water and the recovery of the enzyme was developed. By using the single-stage reactor, the hydrolysis ratio of palm stearin oil was maintained at 80% up to 230 h of operation, and percentage recovery of the enzyme was 98.8%. A countercurrent multistage reactor (three-stage reactor) was developed with the aim of improving the hydrolysis ratio. In the continuous hydrolysis of palm stearin oil using this reactor, the retention time of which was 36 h at each reactor, a high percentage hydrolysis of 95% and an incresed glycerin concentration of up to 30% were observed.