A method of decoding an image, the method comprising: determining a plurality of square maximum coding units in an image based on information about a maximum coding unit extracted from the bitstream, determining a square coding unit which is hierarchically split from a maximum coding unit based on information about coding units extracted from the bitstream, obtaining quantized transformation coefficients of a transformation unit in the coding unit by performing entropy decoding on the bitstream encoded based on the coding unit; 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; obtaining residuals of the transformation unit by performing inverse quantization and inverse transformation on the quantized transformation coefficients of the transformation unit parsed from the bitstream; and performing intra prediction or inter prediction using at least one prediction unit included in the coding unit to generate a predictor, and reconstructing the coding unit using the residuals and the predictor, wherein the at least one prediction unit is one of: a block equal in size to the coding unit, and a block from among a plurality of blocks generated by equally dividing at least one of a height and a width of the coding unit, wherein the transformation unit is one of: a block equal in size to the coding unit, and a block from among a plurality of blocks generated by equally dividing the height and width of the coding unit, characterized in that the method of decoding supports a transformation unit, among the at least one transformation unit, having a size of 2Nx2N that includes four prediction units having a size of NxN. determining a plurality of square maximum coding units in an image based on information about a maximum coding unit extracted from the bitstream, determining a square coding unit which is hierarchically split from a maximum coding unit based on information about coding units extracted from the bitstream, obtaining quantized transformation coefficients of a transformation unit in the coding unit by performing entropy decoding on the bitstream encoded based on the coding unit; 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; obtaining residuals of the transformation unit by performing inverse quantization and inverse transformation on the quantized transformation coefficients of the transformation unit parsed from the bitstream; and performing intra prediction or inter prediction using at least one prediction unit included in the coding unit to generate a predictor, and reconstructing the coding unit using the residuals and the predictor, wherein the at least one prediction unit is one of: a block equal in size to the coding unit, and a block from among a plurality of blocks generated by equally dividing at least one of a height and a width of the coding unit, wherein the transformation unit is one of: a block equal in size to the coding unit, and a block from among a plurality of blocks generated by equally dividing the height and width of the coding unit, characterized in that the method of decoding supports a transformation unit, among the at least one transformation unit, having a size of 2Nx2N that includes four prediction units having a size of NxN.