Serpent is one of the five AES finalists. In our paper, we give solne differentials about Serpent, two of the differentials are a 5-round differential with the probability of 1/207 and a 6-round diffierential with the probability of 1/207. The best known differential before our paper is a 5-round differential with the probability of 1/207 given in [9]. Additionally, we provide all the possible best differentials for some cases about Serpent. From these best differentials, we eonclude that the 16-round best differential is not higher than 1/207 and that the 17-round differential is less than 1/2128.