The purpose of the study was to find out the effect of using Brainstorming strategy in teaching mathematical problem solving on mathematics achievement and creative thinking of ninth female graders . To achieve this, a study guide was prepared a teacher's guide to teach mathematics problem solving in Triangle Geometry Unit using Brainstorming strategy An achievement test in mathematics , along with Mathematical Creativity Test were used after measuring their validity and reliability on a pilot study. The sample of the study consists of (V1) students of grade nine . The sample was divided into two groups, the experimental group based on problem solving using Brainstorming strategy and the control group based on problem solving using the usual method. After treatment , bath achievement test and Mathematical Creativity Test were applied on students of both groups. The findings of this study had shown that the experimental group has excelled the control group in terms of : achievement , fluency , flexibility and the entire creative thinking ability . However the study did not show statistical significant difference between the experimental group and the control group in original ability. The researcher recommends to encourage teachers to use the Brainstorming strategy in teaching and to emphasises the importance of developing the creative thinking in mathematics