This research aims to suggest key design characteristics that are necessary for developing usable e-commerce websites in the Arab world. A comprehensive usability evaluation of four leading Arab e-commerce websites was conducted using the heuristic evaluation method. The results identified major and minor usability problems and major and minor good design characteristics on the selected websites. Based on the results, 51 key design characteristics were suggested. The recommended key design characteristics comprised two levels according to their priority: level one which includes mandatory key design characteristics and level two which includes supplementary design characteristics. The key design characteristics in each level were categorized under specific pages and areas that can be found on any e-commerce website. Such categorizations could direct website evaluators and designers to important pages and areas that should be considered to improve the overall usability of e-commerce websites. The results of this research are particularly important to developing countries which are still facing challenges that may affect the design and accessibility of usable and useful websites. These relate to low speed of accessing the Internet and a lack of website designers who have experience in customers’ needs and websites’ usable design characteristics.