Disclosed herein is a method of encoding/decoding an image. The image decoding method includes decoding information on a quantization matrix from a bitstream, acquiring a quantization matrix of a current block based on the information on the quantization matrix, and dequantizing the current block using the quantization matrix of the current block. The acquiring of the quantization matrix of the current block includes deriving a single identifier using at least one of a size of the current block, a prediction mode or a color component, and acquiring the quantization matrix of the current block based on the single identifier.