Provided are image encoding and decoding methods and apparatuses using weighted bi-prediction. The image decoding method and apparatus according to one embodiment obtain one or more prefixes including a first counter value indicating the number of additional syntax elements subsequent to main syntax elements from a received bitstream, obtain the additional syntax elements including weight information and information about whether to perform weighted bi-prediction on prediction units separated for predicting a current block, based on the one or more prefixes, and generate a prediction block including a prediction value, based on the main syntax elements and the additional syntax elements.