This study aimed to explore the effect of using metacognitive teaching strategy on the mathematics achievement and critical thinking for basic education ninth grade students. The study sample consisted of (54) ninth grade female students from alwafa basic education school. This sample was divided into two groups: An experimental group of (28) students and controlled group of (28) students. We made sure that there is balance between the two groups concerning the previous achievement and the critical thinking, To analyze the data researcher used the following means, standard deviation and t-test. Two main results were concluded from this study. These results are: - There were statistically significant differences at level (a = 0.05) between the means of scores in the achievement test due to the method of teaching favoring the students taught circle by using metacognitive strategy. - There are also differences with statistical meaning at level (a = 0.05) between the geometric means of the two groups results in the critical thinking exam with higher mean for the group who studied the circle mathematics using metacognitive teaching strategy. Based on the results mentioned above, the study strongly recommends using metacognitive strategy in teaching mathematics as it has a major effect in improving mathematical achievement and critical thinking of the students.