Provided is a method and apparatus for controlling a bit-rates in which an amount of generated bits is adjusted according to the complexity of each frame, and a bit-rate within a frame can be further effectively adjusted by applying different quantization parameter (QP) values to respective macro blocks. In the apparatus for controlling a bit-rate, a motion compensated temporal filtering (MCTP) operation is performed for each group of pictures (GOP) in an input scalable layer, and thereafter bits are allocated to respective frames in consideration of frame type and frame complexity. Furthermore, a QP is adaptively determined in the unit of a macro block on the basis of the allocated bits.