This study aims to find the extent of user satisfaction of the marketing mix of the main library at Sultan Qaboos University. It also aims to find out if there is a statistical significant relationship and impact between this user satisfaction and the demand of the library services. The study used the descriptive analysis method by developing an electronic questionnaire and distributed it among the study population. The population consisted of the faculty members, graduate students' cohort 2012 and under graduate students' cohort 2010. The total number of the population was 4,109. A number of 552 questionnaires (13.4% of the population) were retrieved which were valid for analysis. The main findings of the study were: The overall user satisfaction of the marketing mix of the main library was found to reach 73.4% and it is considered to be good. . The highest level of user satisfaction was found to the physical evidence element of the marketing mix with 81.8%, followed by the product element with 78%, then the people element with 77%, then the process element with 75.2%, then the cost element with 72.8%. Both the distribution and the promotion elements were found to have the least user satisfaction with 64.2% for both.Statistical significant relationships were found between the user satisfaction of the Process and the People elements of the marketing mix and the variables of the frequency of the visits of the library and the library website. The variables of the user satisfaction of the marketing mix combined were able to interpret 14.9% of the impact with the benefit variable of the demand. The remaining percentage was attributed to other factors. The study proved what the previous studies found that the user satisfaction of some of the marketing mix elements has an impact on the demand of the library. In this study they were the product, the Promotion, the Process and the People elements. It was concluded that the main library has to know the user needs of information services and develop these elements to fulfill these needs.