In this study, oily waste water was treated by polyvinylpyrrolidone (PVP) grafted polyvinylidene fluoride (PVDF) ultrafiltration membranes. The membranes were prepared stepwise using defluorination, double bond hydration and PVP grafting. The modified membranes were characterized by FTIR and Raman spectroscopy, BET, and water contact angles. Modification mechanism was discussed and compared at the same time. The results showed that PVP was grafted onto PVDF membrane surface via hydrogen bond interaction and the average pore sizes increased slightly while pore structure was not nearly changed after modification. When the PVDF-PVP membranes were applied in oily waste water treatment, their separation performance was improved significantly than that of the PVDF membranes. Besides, fouling mechanism was studied and it could be found that external fouling was the main cause of flux decline. Moreover, flux recovery of the fouled PVDF-PVP membranes after cleaned using 3 wt.% NaOH aqueous solution exceeded 90% and was much superior to that of the fouled PVDF membranes. (C) 2015 Elsevier B.V. All rights reserved.