Objective: To investigate the status and associated factors of sports supplement usage among grade 9 students, so as to provide a scientific basis for targeted supervision and health education regarding sports supplement usage among junior high school students. Methods: From June to September 2025, a stratified cluster random sampling method was used to select 2 261 grade 9 students from 10 provinces (autonomous regions, municipalities) in China. A questionnaire survey was conducted on their sports supplement usage and related factors. The Chi square test was used to compare the usage rates of sports supplements among different groups of students, and binary Logistic regression analysis was employed to investigate the related factors of sports supplement usage among grade 9 students. Results: Totally 59.7% of the grade 9 students used sports supplements. The usage rate (62.5%) was higher among boys than girls (56.3%), higher among students from rural areas and towns/counties (66.5%, 66.2%) than those from urban districts (52.9%), higher among boarding students (65.2%) than non resident students (54.3%), higher among students whose parents occupations were businessmen and workers (fathers: 65.0%, 63.7%; mothers: 63.6%, 61.1%) than those whose parents were farmers and civil servants (fathers: 57.5%, 54.1%; mothers: 58.8%, 55.7%), higher among students with a monthly family income of 5 000- 10 000 yuan (66.3%) than those in other income groups, and higher among students in the high score zone for the entrance physical examination to senior high school (67.7%) than those in the medium and low score zones ( 56.3% , 56.5%) ( χ 2=8.99, 42.21, 27.98, 20.55, 8.20, 22.74, 24.70, respectively, all P <0.05). Binary Logistic regression analysis showed that boys ( OR =1.26), those from rural areas ( OR =1.59), boarding students ( OR =1.36), those with a monthly family income of 5 000- 10 000 yuan ( OR =1.41), and those in the high score zone for entrance physical examination to senior high school ( OR =1.34) were more likely to use sports supplements during the entrance physical examination to senior high school; the probability of sports supplement usage was lower among students whose fathers were civil servants ( OR =0.74) (all P <0.05). Conclusions The usage of sports supplements is relatively common among grade 9 students. Intervention measures should be targeted at specific populations to reduce the risk of misuse.