The objective of this study was to determine the influence of water on the polymerization kinetics, crosslinking structure and dynamic mechanical properties of methacrylate/epoxy polymers cured by visible-light initiated free-radical/cationic ring-opening hybrid polymerization. Water-containing formulations were prepared by adding ~4-7 wt% D2O depending on the water miscibility of monomer resins. The water-containing adhesives were compared with the adhesives photo-cured in the absence of water. The results show an improved degree of conversion for both methacrylates and epoxy by adding water. The rate of the epoxy cationic ring-opening reaction is increased while the rate of free radical polymerization is decreased in the presence of water. The decreased crosslinking density noted in the presence of water suggests that the chain transfer reaction between water and epoxy competes with the hydroxyl-based chain transfer mechanism. There is potential application of this visible-light initiated hybrid polymerization in biomaterials, e.g. dental restorations and tissue engineering scaffolds.