Abstract: Three succinyl xanthan oligosaccharides with different substituting degrees (SA-XG-1, SA-XG-2 and SA-XG-3) were prepared. Their molecular weights determined by GPC method were 7560, 6400 and 7430 u, respectively. Their substituting degree was 0.18, 0.32 and 0.43, respectively. The antibacterial activities of three succinyl xanthan oligosaccharides against Xanthomonas campestris (X. campestris) were investigated by the inhibition zone, minimal inhibitory concentration (MIC) and the influence on the growth of X. campestris. The influence of three succinyl xanthan oligosaccharides on electric conductivity of X. campestris was also determined. The results showed that the inhibition zone was decreased, the MIC was increased, but the damage capability to cell membrane of X. campestris was decreased with the increasing of the substituting degrees, in other words, the SA-XG-1 possessed the best antibacterial activity. The results showed that the antibacterial activity of succinyl xanthan oligosaccharides may be related to the substituting degrees, and the damage capability to cell membrane of X. campestris may be the one of the main antibacterial mechanism of succinyl xanthan oligosaccharides.