The aim of this study was to investigate the extent inclusion of the American National Science Education Content Standards in the Omani science textbooks for grades (5-8). The Sample of the study consisted of all science textbooks for grades (5-8) in basic education in Oman. For the purpose of the study, a content analysis tool was developed. The validity of the tool was conducted by asking a panel of experts to give their comments, and the reliability was calculated using Holsti's Coefficient of categorical reliability giving value of 0.97 between three analysts for a sample of one unit, which was selected randomly from the textbooks analyzed. The data was analyzed statistically and the result, show the following: The Four science textbooks for grades (5-8) included the Physical Science Standard in percentage of (45%), Biological Science Standard in percentage of (30%), and Earth and Space Science Standard in percentage of (13%). The four science textbooks included the Standards of Unifying Concepts and Processes in percentage of (93%), History and Nature of Science Standard in percentage of (27%), and Science in Social and Personal Perspectives Standard in percentage of (13%). Finally, the study Proposed some recommendations such as giving more attention to the American National Science Education Content Standards when developing science curriculum. The study recommended further studies in the same area for other classes.