Background: Cyclooxygenase (COX) inhibition is postulated to restore the immune environment and synergizes with immune checkpoint inhibitors (ICI). The concurrent use of COX inhibitors (COXi) and ICI was associated with longer disease control in metastatic melanoma and non-small cell lung cancer. However, its role in mRCC remains unclear. Methods: We retrospectively reviewed 194 patients with mRCC treated with ICI (PD-(L)1 inhibitors +/- CTLA-4 inhibitors or TKIs) at Moffitt Cancer Center between 6/2014-7/2019. Concurrent use of COXi (aspirin [ASA] or NSAIDs) was defined as at least 3 weeks of COXi use during the first ICI course. Clinical characteristics of both arms were compared using Chi-squared or Kruskal-Wallis Rank Sum test. Time to progression (TTP) and Overall survival (OS) were compared using Kaplan Meier’s estimates. Univariate and multivariate Cox proportional hazards model was performed to evaluate the association between clinical factors, TTP, and OS. Results: Of 194 patients, 126 patients (64.9%) took COXi. Median age was 59.7 years and 80.4% were male. COXi arm had fewer patients with < 1 year from diagnosis to systemic treatment (45.9% vs 69.5%, p = 0.006) and more advanced age (median: 66 years vs 60 years, p = 0.01). IDMC risk group, number of prior therapies, neutrophil to lymphocytes ratio were similar between both arms. Median TTP was 8 months (m) for COXi arm and 12m for ICI only (HR 1.38; 95% CI [0.98, 1.94]). Median OS was 27m for COXi arm and 33m for ICI only (HR 1.05, 95% CI [0.69, 1.59]). Early mortality rate (within 3m of ICI treatments) were similar between both arms. Conclusions: In contrast to melanoma and lung cancer, concurrent use of COXi and ICI did not improve TTP and OS in patients with mRCC. The dual blockade showed a trend for shorter TTP. Further validation studies with larger cohorts are needed to confirm this finding.