With an optical test rig for measuring lubricating films in flattoflat contact,the hydrodynamic films generated by Libase greases were studied.The results indicate that the film building shows complicated behaviors due to the weak replenishment capability of the grease after it leaves the contact and its shearthinning property.The initial lubricating film thickness is decreased significantly with time in the early stage in FlatonFlat conformal contact,then the contact runs at a stable film thickness with starved grease supply,and the grease supply quantity has no influence on this stable film thickness.At a loglog scale,the grease lubricating film and the speed display a linear relationship with a speed index less than that of the base oil.With the increasing of load,the grease presents the film thickness decreasing first and then keeping unchanged.Glycerol shows no obvious influence on the hydrodynamic film thickness of grease.