The aim of this study was to investigate the allelic association of a single nucleotide polymorphism in exon 1 of the cytotoxic T-lymphocyte antigen-4 (CTLA4) gene with rheumatoid arthritis (RA) in Chinese people. One hundred and eighty-six unrelated adults with RA and 203 randomly selected normal adults were studied. All were ethnic Chinese living in Taiwan. The CTLA4 A-G polymorphism was genotyped with a polymerase chain reaction (PCR) and digestion with the restriction enzyme BstEII. The genotype and allele frequencies of CTLA4 in patients with rheumatoid arthritis differed significantly from those of adult controls (#E5/E5#=0.022 and #E5/E5#=0.037, respectively). Genotype CTLA4 49 G/G and allele G were associated with an increased risk of RA (RR=1.72, 95% CI=1.15–2.57, #E5/E5#=0.008; RR=1.39, 95% CI=1.02–1.89, #E5/E5#=0.037, respectively), whereas genotype A/G and allele A were associated with protection against RA (RR=0.58, 95% CI=0.39–0.87, #E5/E5#=0.008 and RR=0.72, 95% CI=0.53–0.98, #E5/E5#=0.037, respectively). We concluded that, the CTLA4 49 A-G polymorphism is associated with RA in Chinese patients from Taiwan.