Boron nitride (BN) shows obvious anti-wear performance as additives in lubricants, ceramics and polymers, however, the strong interlayer interactions lead to the weak anti-friction effect compared to those of carbon-based materials. In this work, we obtained the hydroxylated BN (BNO) via annealing the bulk material in air at high temperature. Utilizing the self-polymerization reactions of dopamine (DA) on the hydroxyls of BNO, the polydopamine (PDA) modified BNO (BNO-PDA) was formed, which has a good dispersity in water. The tribological tests indicate that both the hydroxylation and PDA modification can effectively lower the coefficient of friction (COF) and wear rate of the BN as additives in water, but the letter seems to present lower COF values when the testing time is increased. We also studied the influence of polymerization time on the tribological behaviors of BNO-PDA, and it was concluded that the 6 h modification gained the lowest wear rate and the 24 h modification yielded the lowest average COF value. It is believed that the favorable tribological performance of BNO-PDA as additives in water lubrication is resulted from the improved dispersity and the formation of organic layers on the surface of BN.