Abstract: In the present study, a numerical simulation of laminar natural convection in rectangular undulated enclosures with multiples horizontal partitions was carried out. The partitions have different lengths. They are placed on the undulations of the wavy hot wall. Vertical side walls were kept at constant temperature and horizontal top and bottom walls were insulated. The fluid flow and temperature fields were predicted for different configurations using computer program developed on the basis of finite volume approach. The heat transfer was seriously reduced but there is an optimum value. Effect of cavity aspect ratio, partition length and number of partitions on the heat transfer rate were also investigated.