Objective To explore the expression and significance of miR-21 in patients with primary gout. Methods The patients were divided into 4 groups: 35 acute gout patients (AG), 50 intermittent gout patients (IG), 25 chronic gout patients (CG) and 39 healthy patients. Their peripheral blood were collected and laboratory indexes were recorded. The expression of miR-21 and Nod-like receptor pyrin domain-containing protein 3 (NLRP3) mRNA in the peripheral blood mononuclear cells (PBMCs) was detected by real-time quantitative polymerase chain reaction (RT-qPCR). The blood and clinical data of another 5 healthy volunteers were collected, their peripheral blood was stimulated with 100 μg/ml monosodium urate (MSU) for 1 hour, pho-sphate buffer (PBS) was used as controls, then the expression of microRNA (miR)-21, NLRP3, interleukin (IL)-1β mRNA was detected by RT-qPCR. Rank sum test and spearman correlation analysis were used for data analysis. Results In primary gout patients, the expression of miR-21 in AG [12 ×10-4 (8.0 ×10-4)], IG [9.4 ×10-4 (6.9 ×10-4)], CG [7.3 ×10-4 (5.6 ×10-4)] was significantly higher than that in healthy control group [1.0×10-4(2.0×10-4)] (Z=9.83, P=0.02], while the expression of NLRP3 in AG[0.0444(0.0233)], IG[0.0581(0.0326)], CG[0.0314(0.0198)] was significantly lower than that in healthy control group [0.0886(0.0359)] (Z=13.82, P<0.01). In the primary gout of IG group, the expression of miR-21 was positively correlated with NLRP3 mRNA (r=0.449, P=0.016). After stimulated by 100 μg/ml MSU, the expression of miR-21 of the stimulated group [8.78×10-4(14×10-4)] was higher than that in the control group [6.25×10-4(6×10-4)](Z=-2.203, P<0.05), and the expression of IL-1βin stimulated group [3.06(2.00)] was higher than that in the control group [2.64 (1.22] (Z=-2.203, P<0.05). The level of miR-21 in patients with primary gout was positively correlated with the level of uric acid (UA), glutamic oxaloacetic transaminase (AST) and glutamic pyruvic transaminase (ALT) (r=0.473, 0.639, 0.487, P<0.05). Conclusion The increase of miR-21 in patients with primary gout may be involved in the inflammatory reaction of gout.