The current research aimed to identify the effectiveness of teaching biology using the Universal Design for Learning (UDL) approach in developing deep understanding and self-efficacy among first-year secondary school students. Where the literature and previous research that dealt with each of the entrance (UDL) and deep understanding skills and self-efficacy were surveyed, and the content of a unit of the biology course was studied according to the entrance (the comprehensive design for learning UDL), and the preparation of the deep understanding test and the measure of self-efficacy, and the two research tools were applied before and after on a sample The research used the descriptive method and the experimental method, and the research relied on an experimental design with two groups (the control group), which consisted of (30) students, and the (experimental group), which consisted of (30) students, and the results concluded that there was a statistically significant difference between the mean scores of the group. The experimental group and the control group in the post-application of the deep comprehension test as a whole and its sub-skills separately in favour of the experimental group at the level of (0.5), and there is a statistically significant difference between the mean scores of the experimental group in the pre and post applications of the deep comprehension test as a whole and its sub-skills separately in favour of the application The post-test at level (0.5), and there is a statistically significant difference between the mean scores of the experimental group and the control group in the post-application in the self-efficacy scale as a whole and its sub-dimensions. There is a statistically significant difference between the mean scores of the experimental group in the pre and post-application in the self-efficacy scale as a whole and its sub-dimensions each separately in favour of the post-application at the level of (0.5). Keywords: Universal Design of Learning (UDL) Approach, Deep Understanding Skills, Self-Efficacy.