Abstract: Due to limitations of routine reservoir wettability measurements in low or very low permeability reservoirs,a new method based on stability of water film over rock surface has been suggested.According to physical properties of crude oil,strata water and minerals,with the DLVO theory and the promoted Young-Laplace formula,disjoining pressure of water film over rock surface can be calculated,which stands for stability of water film,hence can be used to judge wettability.Wettability of Athabasca reservoir with high bitumen content in Canada and low permeability reservoir around Daqing Oil Field has been measured,both water-wet.This measurement opens a new way for studies of homogeneous and all kinds of complex heterogeneous wettability of reservoir in the molecular level.