Retention times ( R t ) for acrylates, methacrylates, and vinyl monomers were measured with two different columns (CIS Corasil and C8 LiChrosorb) using reverse-phase HPLC in order to obtain their partition coefficients between 1-octanol and water (log P ) . The log P values of test compounds were determined from the regression curves between RT and log P values of a number of standards using CS LiChrosorb. The log P values obtained in this manner agreed closely with the log P values observed in previous studies. However, the peaks of these compounds were not sharp and some compounds were eluted for more than 10 min. Thus, the measurement of accurate Rt values is tedious. CIS Corasil was therefore used for this experiment in a mobile phase (methanol : water = 85 : 15). The Rt of some methacrylates with P values over 4 were delayed due to the hydrophobic interaction between these compounds and the CIS packing material. However, in the measurable region of the log P values (about -1 to +4), log P correlated linearly with log Rt following two different regression curves: one for aliphatic and aromatic compounds with the functional groups ( r = 0.92), and the other for compounds without these groups ( r = 0.99). It is concluded that log P values of methacrylates widely used in dentistry can be determined easily and accurately by HPLC.