Background: Uterus contractibility is considered a powerful prognostic factor in predicting the embryo transfer outcome. Moreover, uterine contractions are known to be stimulated by prostaglandins which are produced by cyclooxygenase from arachidonic acid. As such, suppressing the inflammatory response and contractions using anti-inflammatory and relaxant agents is expected to result in increased success rate of embryo transfer and artificial insemination. Objective: To investigate the effect of piroxicam administration on the success rate in intrauterine insemination (IUI) cycles in patients presenting with unexplained infertility. Materials and Methods: This randomized, placebo-controlled clinical trial included 260 women with unexplained infertility undergoing IUI cycles. Patients were randomly assigned to receive either piroxicam ten mg/day on days 4-6 after IUI or placebo (control group). The main outcome measures were number of IUI cycles, pregnancy, abortion, and multiple pregnancy rates. Results: The pregnancy rate was found to be 25 (19.2%) and 16 (12.3%) in piroxicam and control groups, respectively (p = 0.039). Five patients (3.8%) in piroxicam group experienced twin pregnancy whereas only three patients (2.3%) in control group had twin pregnancy (p = 0.361). The pregnancy rate per cycle was also significantly higher in those who received piroxicam as compared to controls (11.16 vs. 6.66; p = 0.021). Conclusion: Administration of piroxicam after IUI is associated with decreased number of cycles, as well as increased pregnancy rate and pregnancy rate per cycle in IUI cycles. However, piroxicam did not have any effect on abortion, multiple pregnancy, and ongoing pregnancy rates.