The retention factor corresponding to pure water in reversed-phase high performance chromatography (RP-HPLC), kw, was commonly obtained by extrapolation of retention factor in a mixture of organic modifier and water as mobile phase.In this paper, a relationship of logkw-logk for directly determining kw has been proposed for the first time.With a satisfactory validation, the approach was confirmed to enable easy and accurate evaluation of kw for compounds in question with similar structure to model compounds.Eight PCB congeners with different degree of chlorination were selected as a training set for modeling the logkw-logk correlation on both silica-based C8 and C18 stationary phases to evaluate logkw of sample compounds including seven PCB, six PBB and eight PBDE congeners.