Novel nanofibrous membranes containing reactive carboxyl groups were fabricated from poly- (acrylonitrile-co-maleic acid) (PANCMA) by the electrospinning process. The morphology and fiber diameter were analyzed with field emission scanning electron microscopy. It was found that the fiber diameter could be varied from 100 to 600 nm by changing the solution concentration. Lipase from Candida rugosa was covalently immobilized onto the membrane surface via the activation of carboxyl groups in the presence of 1-ethyl-3- ((dimethylamino)propyl)carbodiimide hydrochloride/N-hydroxylsuccinimide. The properties of the immobilized lipases on the nanofibrous and hollow fiber PANCMA membranes were measured. It was found that, compared with the hollow fiber membrane, the enzyme loading and the activity retention of the immobilized lipase on the nanofibrous membrane increase from 2.36 ( 0.06 to 21.2 ( 0.7 mg/g and from 33.9 to 37.6%, respectively. The kinetic constants of the free and immobilized lipases, Km and Vmax, were assayed. Results indicate that the Vmax values are similar for both immobilized enzymes, while the Km value of the immobilized enzyme decreases from 1.36 on the hollow fiber membrane to 0.98 on the nanofibrous membrane. The studied lipase-immobilized nanofibers can be used as biocatalysts for polyester synthesis and/or in situ formation of nanofiber reinforcement composites.