An ultrafiltration membrane (polyethersulfone, PM10) was surface-modified by treating it with low-temperature plasmas of oxygen, acrylic acid (AA), acetylene, diaminocyclohexane (DACH), and hexamethyldisiloxane (HMDSO). The effects that these modifications have on the filtration efficiency of a membrane in waste water treatment were investigated. The oxygen, AA, and DACH plasma-treated membranes became more hydrophilic. The water contact angles ranged from <10° to 55° depending on the type of plasma and the treatment conditions. The oxygen plasma-treated membranes displayed a higher initial flux (312–429%), but lower rejection (6–91%), than did an untreated membrane. The AA plasma-treated membranes displayed lower or higher initial flux (42–156%), depending upon the treatment conditions, but higher rejection (224–295%) in all cases. The DACH plasma-treated membranes displayed lower initial flux. All of them, especially the AA plasma-treated membrane, displayed improved fouling resistance with either a slower or no flux decline. Acetylene and HMDSO plasma-treated membranes became more hydrophobic and displayed both lower initial flux and lower fouling resistance.