A video encoding method is provided. The method includes: encoding a current region of a video by performing a transformation on the current region by using transformation units in a variable tree-structure which are determined from among transformation units that are hierarchically split from a base transformation unit with respect to the current region and which are generated based on a maximum split level of a transformation unit. The method further includes outputting encoded data of the current region, information about an encoding mode, and transformation-unit hierarchical-structure information including maximum size information and minimum size information of the transformation unit with respect to the video.