The current research aimed to reveal the effectiveness of the Questions cube strategy in developing the skills of Reasoning thinking in mathematics among Preparatory Stage student. The semi experimental curriculum was used for two equal groups (experimental - control), and the research sample consisted of (71) students of the second grade preparatory grade from the Martyr Tarek Zaki is a School preparatory students to the Shebin El-Koum Educational Administration in Menoufia Governorate, divided by (34) students for the experimental group, and 37 students for the control group. A list of the foundations on which the Questions Cube strategy is based, a student's guide, a teacher's guide prepared according to the Questions cube strategy and a test of reasoning thinking skills in the unit “Similarity and Reversal of the Pythagorean theorem and Euclid" were prepared, and the research found a statistically significant difference between the average scores of students the experimental and control groups at the semantic level (0.05) in the post application of Reasoning thinking skills in favor of the experimental group. It also found a statistically significant difference between the average scores of the experimental group students at the semantic level (0.05) in the two applications (pre and post) for the Reasoning thinking skills test in mathematics in favor of post-application.