Provided are method and apparatus for inverse quantizing an image, the method including: determining a quantization step correction value for reducing a quantization error, which is a difference between an inverse quantization coefficient, obtained by inverse quantizing a quantization coefficient, and an original value of the transformation coefficient; and inverse quantizing the quantization coefficient using a second quantization step value, the second quantization step value being obtained by correcting a first quantization step value used for inverse quantizing the quantization coefficient using the determined quantization step correction value.