A directional interpolation method and device for increasing resolution of an image is disclosed. The device includes an input terminal, a memory, a texture analysis module, a texture variance consistence module and an interpolation module. The input terminal receives signals representing the pixels of the image. The memory stores the pixels in row direction. The texture analysis module obtains a monotone variation area by taking the position as a center. The texture variance consistence module computes all directional texture variances in a closest upper and a closest lower rows of pixels within the monotone variation area in the case of taking the position as a center and accordingly finds two pixels having texture variance consistence. The interpolation module finds a value of pixel to be interpolated to the position through a median filter in accordance with the two pixels and their neighbor pixels.