The purpose of the study was to measure the level of intrinsic and extrinsic motivation of the students in the Sultanate of Oman. In addition, the study aimed at exploring differences in intrinsic and extrinsic motivation according to grade level and gender and finding the relationship between these types of motivation and total achievement score in 5", 7th and 9th grade students in Muscat region in general subjects and also in Arabic and mathematic subjects separately. For this purpose the scale of intrinsic and extrinsic motivation was applied on (540) male and female students from 515, 7th and 9th grade of basic education in Muscat region in 2006/2007yr. The academic achievement of the students was obtained from their schools. The result showed that the motivation of the students was above the moderate level for intrinsic motivation and low for the extrinsic motivation. The result also showed while there is a significant differences according to gender in intrinsic motivation, there are no differences between the two genders in extrinsic motivation. Concerning grade level, there is a significant difference in intrinsic motivation between grades 5th and grade 7th and 9th favoring 5th, but there is no differences between 7th and 9th. Similarly, there is a significant differences between 5th and both 7th and 9th grades favoring 7th and 9th grade in extrinsic motivation, but there is no difference between 7h and 9th grade. Furthermore, the study also revealed that there is a significant positive relationship between intrinsic motivation and the students achievement in general subjects and also for Arabic and mathematic. In comparisons, there is a significant negative relationship between extrinsic motivation and the students grades in general subjects and also in Arabic and mathematics.