Purpose: This study performed with goals of determining the Items in designing and developing the user interface of digital libraries' websites and to determine the best digital libraries' websites and discuss their advantages and disadvantages; to analyze and compare digital libraries' websites in developing countries with those in the developed countries. Methodology: to do so, 50 digital libraries' websites were selected by purposive sampling method. By analyzing the level of development of the countries in the sample regarding their digital libraries' websites, 12 websites were classified as belonging to developing and 38 countries to developed counties. Then, their content was studied by using a qualitative content analysis. The study was conducted by using a research-constructed checklist containing 12 main categories and 44 items, whose validity was decided by content validity method. The data was analyzed in SPSS (version 16). Findings: The results showed that in terms of “online resources”, “library collection,” and “navigation”, there is a significant relationship between the digital library' user interface design in both types of countries. Results: The items of “online public access catalogue (OPAC)” and “visits statistics” were observed in more developing countries’ digital libraries' websites. However, the item of “menu and submenus to introduce library' sections” was presented in more developed countries’ digital libraries' websites. Moreover, by analyzing the number of items in the selected websites, “American Memory” with 44 items, “International Children Digital Library” with 40 items, and “California” with 39 items were the best, and “Berkeley Sun Site” with 10 items was the worst website. Despite more and better quality digital libraries in developed countries, the quality of digital libraries websites in developing countries is considerable. In general, some of the newly established websites and lack of use the experience of specialists and librarians, and as a result, lack of information of site designers about users’ needs are some of the reasons for not designing appropriate digital libraries' websites.