The primary purpose of this study was to investigate the effects of gender difference and caffeine supplementation to maximal voluntary isometric contractions (MVIC) and submaximal voluntary isometric contractions (T lim). 10 male (age: 20.10 ± 2.18 years, BMI: 22.23±1.96 kg/m2) and 10 female (age: 19.90±0.99 years, BMI: 21.76±2.65 kg/m2) elite collegiate athletes were recruited. Subjects ingested caffeine (6 mg/kg) or a placebo in a randomized, double-blind, placebo-control, and counter-balanced fashion. MVIC and T lim were measured after supplementations. T lim result was calculated based on the time to exhaustion of isometric contraction with 50% MVIC. Fatigue index (FI%) referred to the MVIC tested 20 s after the cessation of T lim test, and was indexed by the percentage of MVIC decline. No significant interaction effect was found between the gender factor and the supplementation factor for all dependent variables. Compared to the placebo, caffeine supplementation significantly increased MVIC (5.9%) and T lim (15.5%) (p<0.05) whereas it had no significant effect on FI%. This study demonstrates that caffeine supplementation at a 6 mg/kg dosage facilitates performances in MVIC and T lim. The ergogenic effect of caffeine on muscle power and muscle endurance does not show a gender bias.