Provided are a method and apparatus for encoding a video by using block merging and a method and apparatus for decoding a video by using block merging. The method of encoding includes: determining an encoding mode indicating a current data unit for encoding of a picture and an encoding method including prediction encoding performed for the current data unit; determining an occurrence of merging with at least one neighboring data unit based on at least one of the encoding mode and a prediction mode; and determining prediction mode information, merging related information, and prediction related information, and determining encoding information of the data unit including the prediction mode information, the merging related information, and the prediction related information.