PVDF microfiltration membranes were modified by gamma-ray irradiation induced grafting polymerization of 4-vinyl pyridine (4-VP) and then quaternization by n-butyl chloride. The effects of grafting method (simultaneous irradiation, pre-irradiation/UV), grafting conditions (absorbed dose, UV irradiation time, and 4-VP concentration) and quaternization conditions (temperature, time, and concentration of n-butyl chloride) were investigated. It was found that, the grafting degree initially increases with the absorbed dose and then reaches a plateau. The optimal concentration of 4-VP is around 15 wt.%. The ion exchange capacity increases with quaternization temperature, time, and concentration of n-butyl chloride. After modification, the pores size, permeation flux, as well as elongation at break, of quaternized membrane decreases, while the retention coefficient, tensile strength and Young's modulus increase apparently. Upon contacting with the membranes, the Escherichia coli concentration decreases gradually. It is the adsorption mechanism for the pristine membranes whereas contact-killing mechanism for the quatemized membranes. Simultaneous irradiation is more effective than pre-irradiation/UV in the improvement of antibacterial property of membranes. (C) 2013 Elsevier Ltd. All rights reserved.