Provided are a method and apparatus for predicting a motion vector using a global motion vector, an encoder, a decoder, and a decoding method. The motion vector prediction method includes: predicting a global motion vector of the current block; calculating a first motion vector difference between a motion vector of the current block and a motion vector of the adjacent partition, and a second motion vector difference between the motion vector of the current block and the predicted global motion vector of the current block; and predicting, as the motion vector of the current block, a motion vector having a minimum Rate-Distortion (RD) cost, based on the first motion vector difference and the second motion vector difference.