Poor student achievement in science is a global challenge. Sustainable Development Goals 3 and 4 targeting people’s well-being and quality education as well as previous studies linking physical exercises to improved student memory and increased concentration become relevant. This study, therefore, determined the impact of physical fitness activities on students’ Basic Science achievement. The study adopted pretest, posttest, control group quasi-experimental design. Participants included 125 JS2 students from six schools in Ibadan, Oyo State, Nigeria.  Instruments used were stadiometer, gymnasium mats, medicine balls, skipping ropes, cones, stopwatches, weighing scale and Achievement Test in Basic Science (r=.84). The experimental group was exposed to selected science concepts and physical fitness activities simultaneously while the control group was only taught the concepts. Data analysis employed descriptive statistics and Analysis of Covariance. Physical fitness activities had significant effect on students’ achievement (F(1,124)=347.12; P<.05). The experimental group scored higher (x̄=62.58) than control (x̄=53.76). Gender also had significant effect on achievement (F(1,124)=147.89; P<.05) with males performing better (x̄=61.04) than females (x̄=55.29). The interaction effect of treatment and gender on students’ achievement was not significant (F(1,124)=.08; P>.05). Physical fitness activities boosted students’ achievement in Basic Science. Physical fitness activities should, therefore, be implemented in schools.