Deriving an effective facial feature from original face images is a vital step for a successful automatic facial expression recognition. In this paper, we proposed a new feature descriptor, Local Principal Texture Pattern (LPTP), for expression recognition. We compute the LPTP feature, at each pixel, by extracting the principal directions of the local neighborhood, and we code the intensity differences on these directions. The mixture of direction and contrast information makes our descriptor robust against rotation and illumination changes. Consequently, we represent each expression as a distribution of LPTP codes. Our experiments demonstrate the superiority of the proposed feature, on two facial expression databases, over the existing methods.