A method and apparatus for compensating for illumination of a reference block and a method and apparatus for encoding an image, using the illumination compensation method and apparatus, are provided. The method of compensating for illumination of a reference block includes: predicting the mean values of pixels of a current block and a reference block, based on restored values of pixels neighboring the current block, and restored values of pixels neighboring the reference block; and based on the predicted mean value of the pixels of the current block, the predicted mean value of the pixels of the reference block, and the values of the pixels of the current block and the reference block, determining an illumination compensation parameter.