The main objective of this study is to develop and improve the thermal and radiative performance of solar cookers. A solar cooker has been designed, constructed and experimentally analyzed to achieve this goal. The designed system contains three narrow, adjustable flat mirrors that are mounted on a parabolic curved substrate in order to concentrate the reflected solar beam onto the absorber plate. The efficiency of this system depends on many variables that were kept fixed with the exception of the parabolic mirror position and operation time. The response surface method was used as the basis of the design and analysis of the experiments. The analysis of the results provided the mathematical function of the effective and overall efficiencies based on the experimental variables that can be adopted to optimize the mirror positions at any given time. As a result, a new system was developed with adjustable mirrors that yields 32.07% and 35.5% increase in the effective and overall efficiencies, respectively. The results have been validated by variance analysis and comparing theoretical and experimental efficiency. The experiments were carried out in Mashhad, Iran at latitude 37, longitude 54, and a height of 985 m above sea level. (C) 2015 Elsevier Ltd. All rights reserved.