Purpose: To compare the physiological and performance adaptations between periodized and nonperiodized resistance training in women collegiate tennis athletes. Methods: Thirty women (19 ± 1 yr) were assigned to either a periodized resistance training group (P), nonperiodized training group (NV), or a control group (C). Assessments for body composition, anaerobic power, V̇O2max, speed, agility, maximal strength, jump height, tennis-service velocity, and resting serum hormonal concentrations were performed before and after 4, 6, and 9 months of resistance training performed 2-3 d wk-1 Results: Nine months of resistance training resulted in significant increases in fat-free mass; anaerobic power; grip strength; jump height; one-repetition maximum (1-RM) leg press, bench press, and shoulder press; serve, forehand, and backhand ball velocities; and resting serum insulin-like growth factor-1, testosterone, and cortisol concentrations. Percent body fat and V̇O2max decreased significantly in the P and NV groups after training. During the first 6 months, periodized resistance training elicited significantly greater increases in 1-RM leg press (9 ± 2 vs 4.5 ± 2%), bench press (22 ± 5 vs 11 ± 8%), and shoulder press (24 ± 7 vs 18 ± 6%) than the NV group. The absolute 1-RM leg press and shoulder press values in the P group were greater than the NV group after 9 months. Periodized resistance training also resulted in significantly greater improvements in jump height (50 ± 9 vs 37 ± 7%) and serve (29 ± 5 vs 16 ± 4%), forehand (22 ± 3 vs 17 ± 3%), and backhand ball velocities (36 ± 4 vs 14 ± 4%) as compared with nonperiodized training after 9 months. Conclusions: These data demonstrated that periodization of resistance training over 9 months was superior for enhancing strength and motor performance in collegiate women tennis players.