To enhance the contrast and the details of the wireless capsule endoscopy images, which are used to diagnose the status of the human gastrointestinal tracts, we propose a tensor based diffusion method in this paper. After analyzing the structure tensor of the image in RGB color space, we focus on the properties of the nonlinear anisotropic diffusion. Then we design two diffusion strength functions to determine the anisotropic diffusion according to the local characteristics of the wireless capsule endoscopy images. Experimental results on real wireless capsule endoscopy images indicate effective enhancement of details and contrast by our new approach.