Dehydration of a water-acetic acid mixture by pervaporation through a modified poly(4-methyl-1-pentene) (TPX) membrane chemically grafted onto glycidyl methacrylate (TPX-g-PGMA) was investigated. Sulfonation was also used to improve the separation performance of the TPX-g-PGMA membrane. Investigations focused on the effects of feed compositions, feed temperature, degree of grafting, and downstream pressure. Compared with pure TPX membrane, the TPX-g-PGMA membrane and the sulfonated TPX-g-PGMA membrane (TPX-g-PGMAS) effectively improved pervaporation performances. Optimum pervaporation results were obtained using a TPX-g-PGMAS membrane with 13.7% degrees of grafting, giving a separation factor of 73 and a permeation rate of 125 g/m(2).h for an 84 wt% aqueous acetic acid solution.