Aim To study the effect of percutaneous coronary intervention (PCI) on the activities of peripheral blood monocytes and inflammation in patients with stable angina pectoris (SAP). Methods 100 patients with SAP who underwent PCI or coronary angiography (CAG) were randomly divided into PCI group (n=48) and CAG group (n=52). Venous blood samples, from which peripheral blood monocytes were isolated by gradient centrifugation, were collected from all patients at 30 minutes before and 24 hours after PCI or CAG. Interleukin-1β (IL-1β), Interleukin-6 (IL-6), C-reactive protein (CRP), and serum amyloid A (SAA) in supernatant secreted by peripheral blood monocytes at baseline and after stimulation by lipopolysaccharide (LPS) were measured. Serum levels of infammatory biomarkers such as IL-1β, IL-6, CRP, and SAA were also measured and their relations to major adverse cardiovascular events (MACE) at a follow-up period of mean (8±3) months were analysed. Results Compared with those in CAG group, IL-1β (152.3±72.6 ng/L vs 99.4±60.2 ng/L, p<0.01), IL-6 (127.5±44.3 ng/L vs 65.6±36.5 ng/L, p<0.01), and SAA (102.8±54.4 μg/L vs 78.4±49.6 μg/L, p<0.05) in supernatant from peripheral blood monocytes at baseline increased significantly and increased further after lipopolysaccharide stimulation (p<0.01) in PCI group. Meanwhile, IL-1β, IL-6, and SAA secreted by peripheral blood monocytes correlated significantly with the corresponding serum levels respectively (p<0.05 or 0.01). In the follow-up period, although the rate of MACE was higher in the subgroup with higher infammatory biomarkers than that in subgroup with lower inflammatory biomarkers (37.0% vs 19.0%), the differences between them were nonsignificant statistically (p<0.05). Conclusions PCI increased the activities of peripheral blood monocytes and enhanced systemic inflammation in patients with SAP, which maybe associate with poor outcomes.