The paper presents a simple test procedure for determination of design parameters to predict the thermal performance of a box-type solar cooker. A series of out-door experiments were performed on the double-glazed solar cooker of aperture area 0.245 m(2) with a fibre body to obtain two figures of merit, F-1 and F-2. The necessary design parameters-optical efficiency, F'eta(o) and heat capacity, (MC)' of the cooker are calculated using the linear regression analysis of experimental F-2 data for different load of water. Based on the experimental results, a correlation for F-2 as a function of quantity of water (load) is proposed. The close agreement between experimental and calculated F-2 indicates the validity of the correlation. The proposed procedure is then applied to predict the heating characteristic curves of the solar cooker for different load of water. The predicted heating characteristic curves are validated by comparing with the experimental data from a series of cooker testing experiments. The results of present study reveal that F'eta(o) and (MC)' are the critical design parameters required for the prediction of thermal performance of the solar cooker. (c) 2004 Elsevier Ltd. All rights reserved.