This study aimed to investigate the effect of using Cabri- geometry II plus Software in teaching geometry on the geometrical achievement and mathematical proof skills of ninth grade basic education students. The study sample consisted of (59) ninth grade female students from Alwafa basic education school. This sample was divided into two groups: An experimental group of (29) students who were taught by using Cabri. The second was the controll group of (30) students and who were taught by traditional method. We made sure that there is an equivalences between the two groups concerning the previous geometrical achievement and the mathematical proof skills. In order to measure the effect of Cabri on the experimental group, the researcher used the geometrical achievement test and mathematical proof skills. Both tests were reviewed and validated by some specialists. According to the Cronbach- Alpha measuring method, the internal consistency of the geometrical achievement test was (0.81) and the reliability of mathematical proof skills test was (0.78). To analyze data, the researcher used the means, standard deviation, and T-test, This study reached the following findings: - There was statistically significant difference at level (a = 0. 05) between the students means of scores in the geometrical achievement test, favoring the students taught the circle geometry unit by using Cabri. - There was statistically significant difference at level (a = 0. 05) between the students means scores in the mathematical proof skills test, favoring the students taught the circle geometry unit by using Cabri. In the light of these conclusions, the study recommended using Cabri Software for teaching geometry.