An apparatus for decoding an image includes an encoding information extractor which extracts split information indicating whether to split a coding unit of an upper depth into coding units of deeper depths and skip information indicating whether a prediction mode of a current coding unit is a skip mode, from image data and a decoding unit which determines a split structure of a maximum coding unit, according to the split information so that the maximum coding unit is hierarchically split as a depth increases and determines whether the prediction mode of the current coding unit is the skip mode according to the skip information.