Objectives To investigate the differences of serum interleukin-6（ IL-6） level in schizophrenic patients with different illness duration， and the correlation between serum IL-6 level and cognitive impairment. Methods The cross-sectional study was conducted. A total of 65 schizophrenic patients treated with olanzapine monotherapy were enrolled in the study. All the patients were grouped into two groups： the medium course group（ 1-10 years， n=33） and the long course group（ ＞10 years，n=32）. The basic information of patients was collected. Positive and Negative Symptoms Scale（ PANSS） was applied to evaluate the psychiatric symptoms. Cognitive tests were carried out using Trail Making Test（ TMT）， Brief Assessment of Cognition in Schizophrenia（ BACS）， Hopkins Verbal Learning Test-revised（ HVLT-R）， Brief Visuospatial Memory Testrevised（ BVMT-R） and Continuous Performance Test-identical pair test（ CPT-IP）. The serum IL-6 level of all patients were measured. Results （1） The level of IL-6 in the medium course group and the long course group was 3.05（ 1.67， 4.26） pg/ml and 1.62（ 1.52， 3.43） pg/ml respectively， and the difference was statistically significant（ Z=-3.09， P＜ 0.05）.（ 2） There was a negative correlation between IL-6 and the TMT score in the long course group（ r=-0.39，P＜ 0.05）. Conclusions There are significant differences in IL-6 levels among patients with different course of disease. IL-6 levels may be negatively correlated with executive function in patients with course of disease more than 10 years.