Poly(maleic anhydride-co-vinyl acetate) copolymers were prepared by copolymerization in toluene, using AIBN as initiator. Cotton knit fabric was treated with poly(MAn-co-VAc) and the changes in the dye resist property with molecular weight, concentration and curing time was studied. The dye resist ability was evaluated by colorimetric analysis. Higher molecular weight copolymers were more efficient in blocking the dye. This appears to be due to the preferential reaction of the copolymer on the surface of cotton fabric, where the longer chains are more efficient in blocking the penetration of the dye into the fiber, due to the hydrophobic nature of the vinyl acetate comonomer. The blocking effect increased with concentration of the blocking agent padding bath, but yellowing occurred at concentrations above 30 wt%. Although dye resist effect was best when curing time of poly(MAn-co-VAc) was 2 min 30 see, the cotton fabric turned yellowish. Therefore, curing time should be less than 2 min 15 sec in order to avoid yellowing effect and obtain good dye resist property.