A method of decoding an image, the method comprising: determining a plurality of square maximum coding units from an image and determining a square coding unit which is hierarchically split from a maximum coding unit among the plurality of maximum coding units using information about a coding unit, wherein the information about a coding unit is parsed from a bitstream; determining at least one prediction unit which is split from the coding unit using information about a prediction unit, wherein the information about a prediction unit is parsed from the bitstream; determining at least one transformation unit which is split from the coding unit using information about a transformation unit, wherein the information about a transformation unit is parsed from the bitstream; reconstructing residuals by performing inverse quantization and inverse transformation on quantized transformation coefficients of the transformation unit parsed from the bitstream; and performing intra prediction or inter prediction using the at least one prediction unit to generate a predictor, and reconstructing the coding unit using the residuals and the predictor, wherein when a prediction mode is determined to be an inter prediction mode and not an intra prediction mode, the method of decoding supports a transformation unit, among the at least one transformation unit, having a size of 2N x 2N, that includes four prediction units, among the at least one prediction unit, having a size of N x N, wherein the at least one prediction unit is one among blocks including: a block equal in size to the coding unit; and a block among a plurality of blocks generated by equally dividing at least one of height and width of the coding unit, and wherein the transformation unit is one among blocks including: a block equal in size to the coding unit; and a block among a plurality of blocks generated by equally dividing height and width of the coding unit. determining a plurality of square maximum coding units from an image and determining a square coding unit which is hierarchically split from a maximum coding unit among the plurality of maximum coding units using information about a coding unit, wherein the information about a coding unit is parsed from a bitstream; determining at least one prediction unit which is split from the coding unit using information about a prediction unit, wherein the information about a prediction unit is parsed from the bitstream; determining at least one transformation unit which is split from the coding unit using information about a transformation unit, wherein the information about a transformation unit is parsed from the bitstream; reconstructing residuals by performing inverse quantization and inverse transformation on quantized transformation coefficients of the transformation unit parsed from the bitstream; and performing intra prediction or inter prediction using the at least one prediction unit to generate a predictor, and reconstructing the coding unit using the residuals and the predictor, wherein when a prediction mode is determined to be an inter prediction mode and not an intra prediction mode, the method of decoding supports a transformation unit, among the at least one transformation unit, having a size of 2N x 2N, that includes four prediction units, among the at least one prediction unit, having a size of N x N, wherein the at least one prediction unit is one among blocks including: a block equal in size to the coding unit; and a block among a plurality of blocks generated by equally dividing at least one of height and width of the coding unit, and wherein the transformation unit is one among blocks including: a block equal in size to the coding unit; and a block among a plurality of blocks generated by equally dividing height and width of the coding unit.