This study aims at investigating female Students' number sense at sixth grade Basic Education and its relationship with their computational performance. The sample of the study consisted of 451 grade six female students from7 Basic Education schools. The 7 schools were randomly selected from the schools of Batinah South Region in Oman. Data of the study was collected, by the means of two tests : number sense test and computational performance test. The two tests were verified for validity by a panel of arbitrators . Upon their comments, the researcher made the proper modifications. The reliability was also checked by calculating Cronbach Alpha which found to be (0,77) for the number sense test and (0,83) for the computational performance test. After analyzing data , the study found that : 1 ) The female students' number sense at grade six , Basic Education, is very low 2) There is statistically significant difference (a <0.05) in the performance of the female students on the number sense due to their level at the computational performance test (high , middle, low) 3) There is a moderate positive relationship (a <0.05) between the performance of the female students on the number sense test and their performance on the computational performance test. The correlation is (,625). The study ended with some recommendations such as including more activities about number sense in mathematical curriculums and encouraging students to think about the reasonability of their answers and to decide to the extent to which they are suitable and applicable to real life situations.