Heat transfer characteristics and heat storage rate for vertical cylinder packed with paraffin as a latent heat storage material were theoretically studied. Conduction and convection mechanism were applied to the solid and liquid phase, respectively, and the results were compared with that of pure conduction model. The effects of heating temperature, initial solid temperature and aspect ratio on rate of storage were also studied. In the initial stage of melting, the natural convection is nearly restricted by the friction at the wall and the phase boundary. But it is generated when about 40% of solid melts and again it shrinks by the hot liquid situated on the upper part of the cylinder. So overall melting rate is higher then that for pure conduction model. The increase in heating temperature and aspect ratio activates the natural convection, so melting rate becomes higher. And the larger the aspect ratio, the greater the difference between upper and lower size of the solid. In the initial stage of melting, the initial temperature of solid paraffin has great effect on the melting rate, but as melting proceeds its effect lessens gradually.