The electrospun PMMA/O-MMT microfibrous membranes were pretreated by oxygen plasma to create substrates with better adsorption capability. The amount of O-MMT and conditions of plasma treatment were optimized for maximum laccase immobilization on these pretreated surfaces of the microfibrous membranes. The surface morphology and chemistry of the composite microfibrous membranes after plasma treatment and laccase immobilization were investigated by SEM and FTIR. The immobilized laccase showed better resistance to pH and temperature changes than that of the free form laccase, and after 10 successive runs of repeated use, the immobilized laccase still retained 30 % of its initial activity. Reactive X-3B was successfully degraded by both free and immobilized laccase.