This study aimed to explore whether a 16-week Teaching Games for Understanding (TGfU) volleyball intervention could improve primary school students’ physical fitness and body composition. Eighty-eight primary school students (age 13.3 ± 0.3 years) were randomized to a TGfU volleyball intervention group (VG) or a control group (CG). The CG attended three regular physical education (PE) classes per week, while the VG attended two regular PE classes and a TGfU volleyball intervention that was implemented in the third PE class. Body composition components (body weight, body mass index, skinfold thickness, body fat percentage, and muscle mass percentage) and physical fitness (flexibility, vertical jumps (squat and countermovement jump—SJ/CMJ), 30 m sprint, agility, and cardiorespiratory fitness) assessments were performed pre-and post-intervention period. Significant interaction effects between VG and CG and pre- and post-test were found for the sum of five skinfolds (p< 0.0005,ŋp2= 0.168), body fat % (p< 0.0005,ŋp2= 0.200), muscle mass % (p< 0.0005,ŋp2= 0.247), SJ (p= 0.002,ŋp2= 0.103), CMJ (p= 0.001,ŋp2= 0.120), 30 m sprint (p= 0.019,ŋp2= 0.062), agilityT-test (p< 0.0005,ŋp2= 0.238), and VO2max(p< 0.0005,ŋp2= 0.253). Further examination revealed a greater improvement among VG students compared to CG students in certain body composition and physical fitness outcomes. Implementing a TGfU volleyball intervention in the physical education curriculum appears to have effective stimuli for reducing adiposity and promoting physical fitness levels in seventh-grade primary school students.