Abstract: In this paper,one-sided autocorrelation(OSA) and relative autocorrelation sequences(RAS) are studied,and a new algorithm of endpoint detection based on RAS is proposed.As relative autocor-relation has denoising capability,short-time average magnitude of speech signal in double-threshold com-parison is replaced with short-time average magnitude of its RAS,and the short-time average magnitude is substituted for short-time average threshold-crossing rate.Experiments show that the accuracy of endpoint detection is considerably higher than that obtained with the conventional method of double threshold comparison.