The results of FTIR spectra study of OH in olivines from Mengyin kimberlite show that there are more than 60 OH absorption peaks in the range of 3 800～3 000 cm-1. We identified four major spectral features in the OH absorption bands of kimberlitic olivines. One is with νOH in the range of 3 800～3 700 cm-1, which is caused by the vapour of the room circumstance, and can not be regarded as intrinsic or non-intrinsic νOH of the olivines. Another one is with νOH in the range of 3 710～3 620 cm-1, which belongs to three “water”-bearing minerals including serpentine, talc and Mg-bearing amphiboles, which is the non-intrinsic νOH of the olivines. There is the possibility that H in hydrous minerals mainly entered into olivines during post-emplacement processes of the kimberlite magma. The third one is with νOH in the range of 3 620～3 425 cm-1, which originated from H occupying the Si-defect in the olivine structure, forming humite-like defects, and/or the defects that H occupies (Mg,Fe)-depletion, which is certainly attributed to the intrinsic νOH of the olivines. In this case, H possibly entered into olivines following its immersion in the high temperature and rich fluid kimberlite magma in the mantle circumstance. The last one is with νOH in the range of 3 425～3 000 cm-1. In this area, νOH is assigned to fluid inclusions of the olivines, and is the non-intrinsic νOH of olivines. Fluid inclusions can enter into the olivines either during post-emplacement processes of the kimberlite magma or during the periods that olivines were formed in the mantle.