The reaction of o-hydroxybenzyl alcohol with phenyl isocyanate has been investigated in different polar solvents with in situ FT-IR. The rate constants for the reactions of the phenolic hydroxyl group and the aliphatic hydroxyl group were calculated as k1 and k2, respectively. It is found that the phenolic hydroxyl group reacts more easily than the aliphatic hydroxyl group. It is also found that k1 increases with increasing solvent polarity, while the trend of k2 is the opposite. Moreover, the reaction kinetics is second-order with respect to toluene, butyl acetate, cyclohexanone and pyridine, but is first-order with respect to NMP and DMF without distinction for the two kinds of hydroxyl groups.