This study investigated the weight loss (WL) practices of Chinese amateur boxers using the Rapid Weight Loss Questionnaire (RWLQ). A total of 701 (563 males, 138 females) boxers participated in the study and were categorized by sex, age group, and competitive level. Sixty-seven percent of boxers purposefully engaged in WL practices before competition. The average habitual WL was 6.0% (5.8% for juniors and 6.3% for seniors) of body mass (BM), with the average highest WL was 9.5% (9.1% for juniors and 10.1% for seniors) of BM. Most participants (69% for juniors and 84% for seniors) allocated 15+ days for WL before competition. No significant differences in habitual WL%, highest WL%, and rapid weight loss score (RWLS) were found between age groups or competitive levels (all p > 0.05). However, males’ highest WL% and RWLS were significantly higher than females (p < 0.001, p = 0.002, respectively). International boxers began WL later than local boxers (15.5 vs. 14.3 years, p = 0.012). National boxers began WL later than provincial and local boxers (15.6 vs. 14.8 years, p < 0.001; 15.6 vs. 14.3 years, p < 0.001). Increased exercise and training in plastic suits were the most frequently used WL methods. Coaches were identified as the most influential person concerning boxer's WL practices, surpassing doctors or nutritionists. This study found that some WL practices among Chinese boxers differ from those in other sports and countries. Although the prevalence of WL among junior boxers was relatively low, the magnitude of WL was high, warranting more attention in both academic and practical fields.