The asymmetric Kharasch addition reaction was studied by using water as an environmentally friendly solvent. The reaction of styrene with BrCCl3 catalyzed by chiral rhodium species, “RhCl[(–)-DIOP]”, gave the corresponding adduct in moderate chemical and asymmetric yields “on water”, where all the reactants float on water. By reinvestigation of the literature procedure, the chemical and asymmetric yields “on water” were compared with those obtained in organic solvents. The reaction with FeCl2 / (–)- DIOP catalyst was examined to look at the metal effect. Possible reaction mechanisms were proposed based on these results.