This paper proposes a reversible data hiding method based on expanding difference between a pair of neighboring pixels. The proposed method adopts the relation among pixels in a block to determine whether a pair of pixels can be expanded. During the embedding process, the pixels used to determine the expanding status of pixels always remain unchanged and, later, they can be adopted by the decoder to identify the expanding status of a difference when extracting a message. As the expanding status is not saved in the location map, all of the embedding capacities can be used to embed user’s message. In addition, the embedding capacity can be finely tuned by a parameter which determines whether a difference value can be expanded. Experimental results show that both the capacity for embedding user’s message and the image quality are significantly improved, when compared with Tian’s study [IEEE Trans. Circuits Syst. Video Technol., 13(8), pp. 890-896, 2003].