The photografting of a water-insoluble monomer methyl methacrylate (MMA) onto high-density polyethylene (HDPE) initiated by an aliphatic ketone water/alcohol initiating system has been reported. The aliphatic ketones, such as acetone, butanone, and cyclohexanone, could effectively initiate the grafting reaction when they, were mixed with water and ethanol to form homogeneous aliphatic ketone/water/ethanol mixed solvents that Could dissolve the water-insoloble monomer. The nature of aliphatic ketone affected the, grafting; at the same aliphatic ketone/water/ethanol Volume ratio, the grafting system containing acetone or butanone always led to a higher extent of grafting than that containing cyclohexanone none. Water also played a very important role in the grafting reaction; in the tested range, the rate of formation of grafted PMMA on HDPE increased with the increase of water : volume ratio. The grafting of MMA carried out in 5 acetone/40 water/55 ethanol mixed solvent led to the highest extent of grafting. ATR-FTIR characterizations of the grafted samples proved the Successful grafting of MMA onto HDPE. SEM investigations of the HDPE surfaces grafted in different aliphatic ketone/water/ethanol mixed solvents indicate the morphologies of grafted surfaces varied with the mixed solvents used. This study broadened the application fields of the aliphatic ketone/water/alcohol initiating system for photografting. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 418-426, 2009