A new primary school Physical Education (PE) program was launched in 2007 in Turkey, in which the development of health-related physical fitness is one of the most important goals. The purpose of the present study was to investigate the effects of inquiry-based learning model on the fitness components and fitness knowledge test in sixth grade students during the six-week health-related fitness program. Forty-six children from the sixth grade, aged between 11 to 12 years, participated in the study. The experimental group consisted of 23 children who participated in the program held one day a week for an 80-minute session, which was allotted for the Physical Education in the school. The control group (n=23) participated in the routine Physical Education program in the curriculum. One week before and after the study, a physical fitness test was employed in order to assess the subjects and controls. Health-related fitness components (cardio- respiratory endurance, abdominal strength and endurance, flexibility, and body composition) were assessed with the Fitnessgram test battery.