In this paper we present a novel postfiltering algorithm based on the Short-Time Spectral Attenuation (STSA) for enhancing the perceptual quality of audio signals coded at low bit rates. In the proposed algorithm, the quantization noise of coded audio signal is estimated and subtracted from the coded signal by using STSA. For more accurate estimation of the noise spectrum, dithering technique is applied to the quantizer designs. Results show that the proposed algorithm effectively reduces the quantization noise level in the coded audio, resulting in better perceptual quality. The proposed postfiltering algorithm can be implemented in cooperation with existing or future audio coding schemes to improve their performance at low bit rates.