Bouldering (BL) is an independent discipline of sport climbing, with grip strength and endurance as key factors. Although the sport has grown increasingly popular and competitive, limited research has been conducted on commonly used training methods to maximize BL performance. The purpose of this study was to investigate the training effects of 4 weeks of fingerboarding (FB) on grip strength and endurance in competitive BL. Twenty-three highly advanced male boulderers (25.6 ± 4.4 y; 1.78 ± 0.05 m; 70.1 ± 5.4 kg; 6.2 ± 2.8 y climbing; 7b+ Fb mean ability) were randomly allocated to a 4-week FB (n = 11) or BL (n = 12) training regimen. Pretests and posttests (50-min duration) involved (a) handheld dynamometry (GS) to assess grip strength, (b) dead hangs (DH), and (c) intermittent finger hangs (IFH) to assess grip endurance. After the 4-week regimen, GS increased significantly in the FB group (2.5 ± 1.4 kg, p < 0.001) but not in the BL group (1.4 ± 2.8 kg, p = 0.109). The mean increase in DH ranged from 5.4 to 6.7 seconds in the FB group and was significantly (p ≤ 0.05) higher than that in the BL group (3.0-3.9 seconds). Finally, significantly higher IFH gains were observed in the FB group (p = 0.004), with a mean gain of 26 seconds, but not in the BL group (p = 0.168). These results suggest that FB is highly effective in increasing grip strength and endurance in competitive BL.