To study the potential correlations between variances of TNFalpha gene and onset of ankylosing spondylitis in Chinese population, We scanned and analyzed the promoters of TNFalpha genes in 75 AS patients from south of China and found -850 T mutation allele frequency rather high (39.3%).By case-control study, the distribution of TT genotype is significantly higher in AS patients than that in normal subjects (10.7% VS 2.1%,P=0.003); Mutation T allele has a remarkable difference between AS group and normal control (72.2% vs 21.4%,P=2.729 x 10(-9)). The difference in distribution of TX genotype and non -TX genotype is also significant statistically between different genders(male: P=3.42 x 10(-9);female: P=0.001). The result suggests that this variation has a strong association with AS in males and females. No similar reports about the association between AS and the T mutation allele have been acquired. Therefore, our hypothesis can be supported by our results on the whole and the -850 C-->T mutation allele in the region on promoter of TNFalpha gene is likely one of susceptible genes to AS.