The main purpose of this study was to investigate the level of student's achievement in mathematics in Yemen. This study use a sample of 200 male students and 200 female students, chosen from eight government schools on the basis of diversified sampling techniques. A mathematics test which composed of seventy five items that covered geometrical arithmetical concepts, (national, integers and rational) numbers groups, and it is four basic arithmetical operations as well as the equations, and inequalities that were administered to the selected students. The result showed that 35% of the students answered correctly 50% or more items of the test, while 80% of the students made errors in the arithmetic problems, inequalities, equations solutions, division and addition of decimal fractions and Pythagorean Theorem applications. Result also showed that females tend to achieve better results in mathematics than males do. The most common errors made by the students were found to be the basic arithmetical operations for the group of integers and rational numbers as well as the solution of the equations and inequalities. Recommendations for future research were suggested. (Contains 2 tables.)