The study aimed to identify the nature of the dominant organizational culture in the main library at Sultan Qaboos University, as well as to identify the impact of the culture on job performance. The is achieved by studying the effect of the following values on job performance: teamwork, participation in decision making, commitment and respect for the value of time, the encouragement of creativity, and innovation culture. The study was based on a quantitative approach, in which a questionnaire was used for data collection. It consisted of 55 questions based on 6 aspects which represent the variables of the study (organizational culture, teamwork, participation in decision making, commitment and respect for the value of time, encouragement of creativity and innovation, and job performance). The questionnaire was distributed to 82 employees of the main library during the year 2014- 2015 and 72 questionnaires were retrieved. Seventy of questionnaires were analyzed making up 85% of the distributed questionnaires. The Statistical Package for Social Sciences program SPSS was used for analyzing the collected data. The study concluded that the main library at Sultan Qaboos University had the characteristics of strong organizational culture and the culture of the clan and hierarchy(bureaucratic) culture. The Pearson correlation coefficient showed a medium positive relationship between job performance and organizational culture, teamwork, commitment and respect for the value of time and encouragement of creativity and innovation with a significance level < 0.05.Also the findings indicated a low positive relationship between job performance and participation in decision-making. The study sets a group of recommendations include the need for the library to focus on the specific factors affecting the organizational culture in order to strengthen and improve the organizational culture