Objective: To examine the effects of combined aerobic and resistance exercise on health related physical fitness (HPF) and depressive symptoms among senior high school freshmen, and to examine whether HPF mediates the relationship between exercise intervention and depressive symptoms, so as to provide a scientific basis for the coordinated promotion of mental health and physical fitness in schools. Methods: In March 2022, 190 senior high school freshmen from a secondary school of Suzhou in Anhui Province were selected by the random cluster sampling method and randomly assigned to an intervention group ( n = 99) and a control group ( n =91). The control group maintained routine activities, while the intervention group underwent a 10 week combined aerobic and resistance exercise program, three sessions per week, 40 minutes per session. Height, weight, standing long jump, sit ups, 20 m shuttle run, and sit and reach were measured before and after the intervention. Depressive symptoms were assessed using the Center for Epidemiological Studies Depression Scale (CES-D). Analysis of covariance (ANCOVA), Mann-Whitney U test, and Wilcoxon test were employed to compare outcomes before and after the intervention, and mediation analysis was conducted. Results: After controlling for pre test scores, ANCOVA results showed that compared with the control group, the intervention group demonstrated the following post intervention changes: a lower body mass index of 0.1 kg/m 2 among girls; higher standing long jump (13.2 cm for boys, 7.4 cm for girls), higher sit ups (5.5 reps for boys, 3.7 reps for girls), higher 20 m shuttle run (7.4 times for boys, 5.1 times for girls), and higher sit and reach (3.2 cm for boys, 0.4 cm for girls) ( F =17.88-84.44); and lower CES-D scores (5.5 for boys, 4.0 for girls) ( Z =-2.51, -2.06) (all P <0.05). The indirect effect of HPF in the relationship between combined aerobic and resistance exercise and depressive symptoms was -2.11, supporting a partial mediation effect ( P < 0.01 ). Conclusions Combined aerobic and resistance exercise improves HPF and alleviates depressive symptoms to varying degrees among senior high school freshmen. HPF served as a partial mediator through which exercise intervention reduces depressive symptoms.