Based on the framework of interest, studies have shown that situational interest possesses strong motivation potential for students in physical education. Understanding how teachers can use situational interest in a classroom context is critical to motivate students. However, such investigations have been exclusively conducted in the United States and little is known about situational interest in other contexts. Grounded specifically in the French physical education curriculum, the purpose of this study was to investigate the relationships between the five situational interest sources (instant enjoyment, exploration intention, attention demand, challenge and novelty) and total interest, to demonstrate which sources could be related to total interest and to determine possible mediators’ effects among sources. Students (n = 601; M _age = 14.37; range 11–18 years; SD = 1.96; 51.4% boys) from 25 classes in six secondary schools participated in the study. They responded to the French situational interest scale after practising learning tasks in regular physical education lessons. On the basis of multiple-regression and mediation analyses, a structural equation model was formed to map out the meaningfulness of the relationships among situational interest sources and the total interest. Our results showed that instant enjoyment and exploration intention have direct and positive effects on total interest. In addition, these sources mediated the effects from attention demand and challenge toward the total interest. These results indicated that an effective way to motivate students in physical education is to build motivational components into the course content, especially those which enhance situational interest.