Sprint freestyle performance is influenced by lower-body propulsion, kick efficiency, and ankle plantarflexion range of motion. Swim fins are widely used to increase kicking intensity during training; however, evidence regarding the effectiveness of structured fin-based training in adolescent competitive swimmers remains limited. This study aimed to evaluate the effect of a systematic fin-based kick training program on 50-m freestyle sprint performance. A one-group pretest–posttest design was conducted involving nine male competitive swimmers aged 12–17 years who were recruited from a swimming club through purposive sampling. Participants completed a six-week intervention consisting of 16 training sessions (three sessions per week, approximately 90 minutes each). The training program included fin-assisted kick drills, sprint drills, board kick drills, and streamline kick drills. Freestyle 50-m sprint time was measured before and after the intervention. Data normality was assessed using the Shapiro–Wilk test, while pre- and post-intervention differences were analyzed using a paired-samples t-test. The results showed a significant reduction in mean sprint time from 32.40 ± 7.32 s to 31.74 ± 7.24 s, representing a mean improvement of 0.66 s (2.3%; p < .001). These findings indicate that a structured fin-based kick training program may provide a practical method for improving sprint freestyle performance by enhancing lower-body propulsion. Nevertheless, the lack of a control group limits the ability to attribute the observed improvements solely to the intervention. Future randomized controlled studies with larger samples are recommended to confirm these findings.