A numerical computation is carried out to study the interaction of rotation and natural convection inside a finite horizontal cylinder. The natural convection is due to differential heating on the two ends, while the rotation is along the axis of the horizontal cylinder. The aspect ratio, length of the cylinder to its radius, is 2.0. The Grashof number is fixed at 1.43 x 10' with air as a working fluid. The effect of rotation is examined with Gr/Re2 from 7.0 x IO-'to CO, which covers the range from rotation dominated flow to buoyancy dominated flow. It is found that when rotational speed is relatively small or Gr/Re* >> 1, the effect of rotation is t o render the spatial heat flux distribution more uniform. As the rotational speed increases, the heat transfer rate distribution on'the end surfaces is more homogenous and its level is also reduced. When the rotational speed is sufficiently high (Gr/Re' << l.O), heat transfer is by conduction only and the whole fluid inside the enclosure rotates as a rigid body. It is shown that there exists a rotation speed range in which one can have both relatively high and uniform heat transfer rates on the end walls.