This study aimed to provide foundational data for adolescent weightlifters by analyzing the physical fitness characteristics of elite middle school weightlifters according to weight class and examining the correlations between lumbar strength and various physical fitness components. A total of 62 elite male middle school weightlifters (age: 13.6 ± 1.0 years) were classified into lightweight (n = 25), middleweight (n = 21), and heavyweight (n = 16) groups. Measurements included body composition, basic physical fitness, lumbar and lower-limb strength, lumbar and lower-limb power, and anaerobic power. Results showed significant differences among groups in height, weight, BMI, and body fat percentage (p<.01), with the heavyweight group displaying the highest values. In basic physical fitness, grip strength, back strength, reaction time, sit-and-reach, and dynamic balance differed significantly by group (p<.05), while hand-eye coordination did not (p>.05). Although the absolute values of trunk and lower-limb strength were higher in the heavyweight group, body weight-adjusted values were significantly lower compared to the other groups (p<.05). Similarly, anaerobic power was higher in absolute terms for the heavyweight group but showed no significant differences when normalized to body weight (p>.05). Lumbar strength showed significant correlations with vertical jump, dynamic balance, lower-limb strength, and anaerobic power (p<.05). These findings suggest that physical fitness characteristics differ by weight class among elite middle school weightlifters and highlight the critical role of core strength in explosive power, balance, and overall performance. Tailored training programs based on weight class and developmental stage are recommended for optimizing performance and preventing injuries in this population.