The present study describes an experiment on natural convective heat transfer from horizontal cylinders to silicone oil or water in a rectangular enclosure. By means of the visualization of temperature distributions by a liquid-crystal suspension method and the measurements of temperature by thermo-couples, obvious thermal stratification and circulating flow were observed. The heat transfer coefficient for the cylinders with thermal stratification and circular flow are estimated. In case of those are weak, as fluid temperature which was located appropriately is assigned to reference, relationship between Rayleigh number and Nusselt number agree with the relation of previous works on natural convection. If those are effective, it is difficult to put in order by former equations.