Abstract: Objective: To compare game performance and physiological load in 3×3 basketball across environments with different heat-stress risk levels and to describe responses after 7 days of heat acclimation. Methods: Technical statistics from 206 games at three tournaments and physiological monitoring data from 14 women's 3×3 basketball players were analyzed. Sites were classified as very low, moderate, or high risk according to wet-bulb globe temperature (WBGT); seven athletes completed 7 days of heat acclimation (35℃, 70% relative humidity, once daily). Results: Field-goal, 1-point, and free-throw percentages were lower at the moderate- and high-risk sites than at the very-low-risk site; free-throw percentage dropped from 73.76% to 47.80% and 47.70% (P<0.05). At the high-risk site, mean heart rate reached (176.35±6.45) beats per minute and accumulated time above 90% of maximum heart rate was (741.15±266.76) seconds, about twice that of the other two sites (P<0.001). Post-game peak core temperature did not differ among the three groups. After heat acclimation, heart rates during exercise, hot-environment rest, and recovery were reduced (P<0.05), whereas core temperature, fluid intake, and sweat rate did not change significantly. Serum HIF-1α and HSP-72 concentrations were higher and serum LDH activity was lower 3 days after the final session (P<0.05); HIF-1α and HSP-72 returned toward baseline by day 21. Conclusion: Detrimental effects of heat stress on shooting efficiency and heart-rate load in 3×3 basketball already emerged at the moderate WBGT risk level; free-throw percentage and accumulated high-heart-rate time are sensitive monitoring indicators. Seven days of heat acclimation can induce early cardiovascular and selected serum biochemical adaptations, but thermoregulatory adaptation was not established within 7 days.