Background: Pentraxin 3 (PTX3) is an inflammatory marker, a member of long pentraxin superfamily that has an important role in inflammation and immunity. Objectives: The aim of this study was to measure serum pentraxin 3 levels in RA patients and evaluate their relation with different disease parameters. Methods: We measured serum PTX3 levels in 40 women with RA and 40 female control subjects. PTX3concentrations were measures by ELISA. Results: Median serum level of pentrexin 3 was significantly higher in RA patients compared to healthy controls (36.4 ng /ml vs 12.4 ng /ml respectively) (p < 0.001). There was a significant difference in serum PTX3 levels according to the disease activity grades. PTX3 concentration was also significantly correlated with ESR(r = 0.506, p=0.001), CRP(r = 0.780, p < 0.001) and Larsen Score (r = 0.784, p < 0.001). There was no significant difference in serum PTX3 levels and RF& anti-CCP positive and negative patients (P >0.05). No significant correlation (p>0.05) was found between serum Pentraxin-3 and age (r = 0.095), BMI(r = 0.059), disease duration (r = 0.048) and RF titer(r = 0.240). Conclusions: PTX3 can be considered as a sensitive non-invasive biomarker reflecting the disease activity and radiological damage in RA patients.