Abstract: Using an optical interferometry system, wall slippage under high pressure conditions was studied experimenally. The slip length can be quantified by tracing the movement of the entrapped dimple core. The experimental results show that the dimple core moved at a speed which was lower than the entrainment speed under disc sliding conditions and larger than that in the case of ball sliding. The experimental observation indicates that the wall slippage occured on the disc surface. The slip length and shear rate can be obtained by analyzing the movement of the dimple core. The measuring results demonstrate that the slip length increased with increasing film thickness, initial dimple core pressure and lubricant viscosity increasing but decreased with increasing entrainment speed.