Provided are methods and apparatuses for entropy-encoding and entropy-decoding an image. The method for entropy-encoding an image includes operations of arithmetically encoding a binary value of a current coding symbol, by using a probability of a predefined binary value which is determined based on previously-coded symbols that are encoded before the current coding symbol; and updating the probability of the predefined binary value by using a plurality of scaling factors, according to the binary value of the current coding symbol.