The purpose of this study was to compare the acute effects of back squat exercise with or without elastic band on countermovement jump performance. Thirteen collegiate male basketball players (age: 20.5 ± 0.9 years; height: 188.5 ± 8.5 cm; body mass: 82.8 ± 12.9 kg) completed 5 familiarization and 4 experimental sessions separated by at least 48 hours. In the experimental sessions, the order of the conditions was randomized so that the participants performed 1 set of 3 repetitions of barbell back squat at 85% of their one-repetition maximum (1-RM), 1 set of 3 repetitions of back squat at 85% 1-RM with 20% variable resistance training (VRT), 30%VRT, or 40%VRT of the total load coming from the elastic band. Countermovement jump performance was assessed before (baseline), 30 seconds, 3 minutes, 6 minutes, and 9 minutes following each condition. Jump height, rate of force development, peak power, and vastus lateralis, vastus medialis, and medial gastrocnemius electromyography data were collected. Compared with the baseline, 30%VRT significantly improved jump height at 3 minutes post-exercise by 1.3 cm (P < 0.001) and 6 minutes post-exercise by 1.2 cm (P = 0.005); 40%VRT significantly improved jump height from 30 seconds up to the 9th minute (1.2 to 1.9 cm, P ≤ 0.036). The superior jump height was also accompanied by improved kinetic and electromyography data. No significant changes were observed in the barbell back squat and 20%VRT conditions. In conclusion, back squat at 85% 1-RM with 40% elastic band resistance led to superior vertical jump performance with an optimal time window of 3 minutes.