This paper describes the influences which govern solar box cookers: HS 7534, HS 7033 and the newest design HS 5521. The best of solar cooker, type HS 7033 gave oven temperature of 202°C between 12:00 and 12:45 p.m. on October 7, 1997. Thirty-four units of this type have been field tested since September 1997. It was found that these solar cookers have a good heat storage capability, therefore they can be used for consecutive cooking. The optimization of the size, the aperture area, the insulator thickness, the oven volume and the reflector area leads to a new design, type HS 5521. Its volume is only 35% of the volume of HS 7033 and cheaper. The performance comparison of the last two solar cookers are described based on the data collected during testing with and without load. The HS 5521 has the same heat collection rate and is able to cook as fast as HS 7033. The performance of three types of solar cookers available in Indonesia was analyzed and compared. Field tests demonstrated that type HS 7033 feature good heat storage capability and can be used for consecutive cooking. Type HS 5521 was designed on the basis of size, aperture area, insulator thickness, oven volume, and reflector area optimization of HS 7033 specifications. The new design has a volume only 35% that of HS 7033 and is less expensive to construct and operate. HS 5521 also has the same heat collection rate and can cook as fast as HS 7033. (from World Renewable Energy Conf Proceedings, Perth, Australia, Feb 99).