A method of decoding an image, the method comprising: obtaining a current coding unit hierarchically split from a square maximum coding unit according to a current depth, whereby the current coding unit has a square shape; obtaining a current prediction unit from the current coding unit by equally splitting a width or a height of the current coding unit by two, or by equally splitting both the height and the width of the current coding unit by two, or by determining the current coding unit as the current prediction unit; obtaining a prediction mode information of the current prediction unit in the current coding unit from a bitstream; when the prediction mode information indicates that a prediction mode of the current prediction unit is inter-prediction and that a motion vector predictor is determined based on a motion vector predictor information indicating a motion vector predictor of the current prediction unit, receiving the motion vector predictor information, from the bitstream; determining motion vector predictor candidates from among motion vectors of previously decoded prediction units adjacent to the current prediction unit; determining a motion vector predictor of the current prediction unit which is one motion vector selected from among the motion vector predictor candidates based on the motion vector predictor information; and obtaining a motion vector of the current prediction unit based on the motion vector predictor and a differential vector obtained from the bitstream, wherein the previously decoded prediction units comprise a first prediction unit located on a lower-left side of the current prediction unit. obtaining a current coding unit hierarchically split from a square maximum coding unit according to a current depth, whereby the current coding unit has a square shape; obtaining a current prediction unit from the current coding unit by equally splitting a width or a height of the current coding unit by two, or by equally splitting both the height and the width of the current coding unit by two, or by determining the current coding unit as the current prediction unit; obtaining a prediction mode information of the current prediction unit in the current coding unit from a bitstream; when the prediction mode information indicates that a prediction mode of the current prediction unit is inter-prediction and that a motion vector predictor is determined based on a motion vector predictor information indicating a motion vector predictor of the current prediction unit, receiving the motion vector predictor information, from the bitstream; determining motion vector predictor candidates from among motion vectors of previously decoded prediction units adjacent to the current prediction unit; determining a motion vector predictor of the current prediction unit which is one motion vector selected from among the motion vector predictor candidates based on the motion vector predictor information; and obtaining a motion vector of the current prediction unit based on the motion vector predictor and a differential vector obtained from the bitstream, wherein the previously decoded prediction units comprise a first prediction unit located on a lower-left side of the current prediction unit.