A performance study of the box-type solar cooker was made with special emphasis on the shape of lid of the utensils used in a solar cooker. The study revealed that the performance of a solar cooker can be improved if a utensil with a concave shape lid is used instead of a plain lid, generally provided with the solar cooker. The stagnation temperature for a utensil having a concave lid was about 2-7% more than the utensil with a normal lid. The time required for heating the water up to the same temperature in both the utensils was reduced by about 1-13% when a concave shape lid was used.