Abstract : Partial answers have been provided in the real-time literature to the question whether preemptive systems are better than non-preemptive systems. This question has been investigated by many authors according to several points of view and it still remains open. Compared to preemptive real-time scheduling, non-preemptive real-time scheduling and the corresponding schedulability analyses have received considerable less attention in the research community. However, non-preemptive scheduling is widely used in industry, and it may be preferable to preemptive scheduling for numerous reasons. This approach is specially well suited in the case of hard real-time systems on the one hand where missing deadlines leads to catastrophic situations, and on the other hand where resources must not be wasted. In this paper, we firstly present the non-preemptive model of task with strict period, then we propose a schedulability condition for a set of such tasks, and finally we give a scheduling heuristic based on this condition.