Aim To investigate the effect of obstructive sleep apnea syndrome (OSAS) on peripheral blood C1q level in patients with unstable angina pectoris (UAP) and its correlation with platelet aggregation rate (PAR) after percutaneous coronary intervention (PCI). Methods 182 patients with UAP who underwent PCI treatment in Beijing Anzhen Hospital from July 2018 to July 2019 were continuously selected. All patients underwent polysomnography. Patients with apnea hypopnea index (AHI)≥15 were taken as the OSAS group (n＝92), and patients with AHI＜15 were taken as the control group (n＝90). Serum C1q level and adenosine diphosphate induced PAR were detected. The relationship between AHI, serum C1q and PAR was analyzed. Results The serum C1q level in OSAS group was significantly higher than that in control group (176.00 (174.8,9.26) mg/L vs 174.50 (167.5,0.76) mg/L, P＝0.030). One month after PCI, PAR in OSAS group was significantly higher than that in control group ((51.36%±19.34%) vs (42.56%±22.23%), P＝0.007). Spearman correlation analysis showed that AHI and serum C1q were positively correlated with PAR (r＝0.219, P＝0.003; r＝0.634, P＜0.001). Multivariable linear regression analysis showed that AHI and serum C1q were independent factors influencing the increase of PAR after PCI (P＝0.036; P＜0.001). Conclusions Serum C1q is significantly increased in UAP patients with OSAS. AHI and C1q are the influencing factors of high platelet reactivity in UAP patients with OSAS one month after PCI.