OBJECTIVE: It remains controversial whether 6-thioguanine nucleotide (6-TGN)-based dose adjusting can be beneficial in azathioprine (AZA) therapy. This study is designed to assess the role of 6-TGN concentrations in maintaining clinical remission in Chinese patients with Crohn's disease (CD). MATERIAL AND METHOD: We performed a prospective observational study and collected data of CD patients in the First Affiliated Hospital of Anhui Medical University from June 2013 to April 2014. Demographic material, CD activity index, 6-TGN concentration, and laboratory tests were recorded at baseline and at each visit. In addition, 6-TGN was measured when drug adverse effects occurred. All patients achieved maintenance stage were administered a stable AZA dose at least 3 months before enrollment and were followed up at least 12 months. Thiopurine S-methyltransferase (TPMT) genotype was measured before AZA treatment. RESULTS: Sixty-nine patients receiving maintenance therapy were analyzed. A positive correlation was found between 6-TGN levels and AZA dose (r = 0.258, p = 0.032). The mean 6-TGN concentration was 302.06 +/- 115.84 in the remission group vs. 264.94 +/- 164.53 pmol/8 x 10(8) RBC in those with active disease (t = 0.847, p = 0.40), and 197.74 +/- 66.54 pmol/8 x 10(8) RBC in patients who relapsed vs. 310.26 +/- 122.38 pmol/8 x 10(8) RBC for those in sustained remission (t= -2.541, p = 0.013). In the leukopenia group, the 6-TGN concentration was 469.11 +/- 115.53 pmol/8 x 10(8) RBC vs. 257.31 +/- 83.74 pmol/8 x 10(8) RBC in the non-leukopenia group (t = 7.622, p < 0.001). There was a significant negative correlation between leukocyte count and 6-TGN concentration (r= -0.326, p = 0.006). CONCLUSIONS: 6-TGN measurement is a helpful method of preventing disease relapse and avoiding leukopenia in individual azathioprine maintenance therapy.