A single-channel blind dereverberation algorithm is proposed in this letter for distant-talking speech recognition. The proposed method is based on spectral subtraction (SS) method, in which the spectrum of a late reverberant signal is estimated using a delayed and attenuated version of the reverberant signal. Through some assumptions, the conventional SS method regards the attenuation weight as a constant that is a function of reverberation time. However, these assumptions are not valid in real situations, and the ideal weight varies with the frame. Therefore, in the proposed method, the variable weight sequence is estimated using Viterbi decoding scheme based on the reverberation model. This weight sequence is then substituted for the fixed weight in the conventional SS method without explicitly estimating the reverberation time. The proposed method performs better than the conventional SS method in both isolated word recognition and connected digit recognition experiments in reverberant environments.