Objective · To explore and analyze the characteristics of nicotinic acid skin sensitivity in clinical high risk (CHR) population of psychosis. Methods · One hundred and five patients with CHR of psychosis (CHR group) and fifty-one patients with first episode schizophrenia (FES) (FES group) in Shanghai Mental Health Center, Shanghai Jiao Tong University School of Medicine Jun. 2016 to Jun. 2018, and fifty-four healthy controls (HC group) were included. The patients of CHR group met the criteria of prodromal syndromes, and the patients of FES group met the diagnostic criteria of Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition). The patients of HC group were matched with CHR group in age and gender . The niacin skin flush of the three groups were detected. The niacin skin flush scores of the three groups were comparedsingle factor repeated measurement variance analysis (MANOVA). The niacin flush negative rates of the three groups were comparedChi-square test. Results · Compared with HC group, the niacin skin flush of CHR group and FES group reduced at different concentrations and time points. MANOVA showed a significant main group effect of niacin skin flush (F1.746, P0.009). There were no significant group × concentration interaction (F1.628, P0.138) and group × time interaction (F0.851, P0.531). Compared with HC group, the niacin total flush scores of CHR group were lower (t-2.697, P0.008). The significant differences of the proportion of patients with negative niacin reaction among the three groups were found for the concentration of 0.1 mol/L at 5 min (χ216.709, P0.000) and 0.001 mol/L at 20 min (χ26.380, P0.041). Conclusion · The reduction of the niacin skin flush can occur not only in the patients with schizophrenia but also in the CHR of psychosis in the precursor phase. Niacin skin flush may be an early biological marker of schizophrenia.