Selective hydrolysis of borage oil by Candida rugosa lipase immobilized on microporous polypropylene was carried out in an iso-octane-water two-phase system in order to obtain glycerides rich in gamma-linolenic acid (GLA). Lipase was immobilized on hydrophobic microporous polypropylene supports by physical adsorption. gamma-linolenic acid content in the unhydrolyzed acylglycerols could be raised to 51.7 mol% from an initial content of 23.6 mol% in borage oil with a yield of 59%. A simplified kinetic model was proposed for this selective hydrolysis. The Michaelis constant K-M and the maximal-rate constant V-max are 0.107 M and 393.9 U/mg-protein, respectively. Product inhibition with a dissociation constant of the enzyme-product complex K-I = 25 mM was confirmed. Some properties of the immobilized lipase were also examined.