Objective To investigate the differential expression of microRNA (miRNA) in schizophrenia (SZ) patients,and explore the comorbidity of SZ and depression disorder based upon miRNA expression.Methods Affymetrix array analysis was used to investigate the differentially expressed miRNA in SZ patients firstly,and then quantitative real-time polymerase chain reaction (qRT-PCR) was further carried out to confirm the selected miRNA in peripheral blood mononuclear cells of 40 SZ patients,whom were administered by Positive and Negative Syndrome Scale (PANSS) and the selected miRNAs in depression disorder patients has also been confirmed by Affymetrix array analysis and qRT-PCR in our previous studies.Results Affymetrix array analysis indicated that there existed 33 miRNAs which differentially expressed (32 up-regulated and 1 down-regulated) compared with normal controls.qRT-PCR results suggested that the expression of 8 miRNAs (miR-1273d,miR-1303,miR-3064-5p,miR3131,miR-3687,miR-4428,miR-4725-3p and miR-5096) were significantly up-regulated in SZ;the miRNA differentially expressed in depression disorder patients also had differential expression in SZ patients (P＜0.05).There were significant correlation between the miRNAs differentially expressed in depression disorder patients and in SZ patients (P＜0.01).MiR-1972 differentially expressed in depression disorder patients had significant positive correlation with the positive symptoms of PANSS (P＜0.05),and miR-26b was positively correlated with composite factor (P＜0.05).Conclusion Comorbidity of SZ and depression disorder is observed not only on the clinical symptoms,but on the molecular genetic basis.