An apparatus for encoding image information using a tree structure performs a method by: encoding a partition flag indicating whether each node, starting from a node of an uppermost layer of the tree structure, is divided into nodes of a lower layer; encoding image information of a block corresponding to a node which is not further divided; and encoding additional information including first information on a minimum block size and second information on a difference between the minimum block size and a maximum block size, wherein the first and second information are used for identifying the maximum block size corresponding to the node of the uppermost layer.