Purpose Strenuous exercise induces inflammation and muscle damage. Turmeric ( Curcuma longa L. ) is a widely used spice that exhibits potent anti-inflammatory response and appears to decrease indirect markers of muscle damage. A randomized, double-blind, placebo-controlled trial was conducted to evaluate the effects of Curcuma longa L. extract (CLE) on inflammation and muscle damage after a half-marathon race. Methods Twenty-eight healthy, normal-weight men were randomly assigned to one of two groups: (1) CLE (3 capsules per day, 500 mg each); or (2) placebo (PLA, 3 capsules per day, 500 mg of microcrystalline cellulose). Participants received the intervention for 4 weeks and immediately before and after the half-marathon race. Creatine kinase, lactate dehydrogenase, alanine aminotransferase, aspartate aminotransferase, myoglobin, interleukins 6 and 10 were assessed at baseline, immediately before, after, and at 2, 24, and 48 h after the half-marathon race. Results The half-marathon race increased markers of inflammation and muscle damage. A greater increase in interleukin-10 was observed in the CLE group immediately after the competition compared to the PLA group (7.54 ± 1.45 vs 5.25 ± 0.59 pg/mL; p  < 0.05; d  = 0.55). Myoglobin concentration was lower 2 h after the race in participants from the CLE group compared to the PLA group (62.10 ± 8.26 vs 107.85 ± 18.45 ng/mL; p  = 0.01; d  = 0.86). Conclusion Curcuma longa L. extract supplementation leads to an increase in IL-10 and decreased myoglobin in recreational male runners after a half-marathon race. Trial registration number U1111-1179-6335, February 13, 2016.