OBJECTIVE： To explore the clinical related factors of leucopenia induced by azathioprine in the treatment of inflammatory bowel disease （IBD）. METHODS： Clinical information of 114 IBD patients were collected from our hospital during Jan. 2013-Mar. 2015. Steady concentration of AZA metabolite 6-thioguanine （6-TGNs） in red blood cell was determined by HPLC. The correlation of patient’s gender， age， diseases， AZA daily dose and blood concentration of 6-TGNs with leucopenia induced by AZA were investigated. The optimal critical value of leucopenia could be predicted with ROC curves. RESULTS： Among 114 IBD patients， 40 patients suffered from leucopenia （35.1％）. There was no statistical significance in the proportion of leucopenia among patients with different age， gender， diseases and AZA daily dose （P＞0.05）. There was statistical significance in the proportion of leucopenia among patients with different concentrations of 6-TGNs （P＜0.05）. Mean blood concentration of 6-TGNs in leukopenia patients [（407.82±262.88）pmol/（8×108） RBC] was higher than patients with normal leukocyte level [（275.85±118.37） pmol/（8×108） RBC]， with statistical significance （P＜0.05）. ROC curve predicted that the optimal critical value of leucopenia was blood concentration of 6-TGNs＞291.04 pmol/（8×108）RBC. CONCLUSIONS： AZA induced leucopenia may be related to the concentration of 6-TGNs in red blood cell of IBD patients， and high concentration of 6-TGNs is risk factors of leucopenia. Clinicians can provide AZA individual treatment for IBD patient to reduce the occurrence of ?leucopenia according to routine blood test and the concentration of 6-TGNs.