Abstract: The aim of the current research is to identify (the relationship between deep understanding skills and mathematical modeling among fifth grade students) the research sample consisted of (411) male and female students of the fifth grade of biology distributed over the General Directorates of Education in Baghdad / Al-Rusafa / 2 / and Al-Karkh / 1 /, and two research tools were built: 1- A test of deep understanding skills, consisting of (20) test items and a scale for two skills. 2- The second test consists of (24) test items distributed among (18) essay items and (6) objective items. The psychometric properties of validity, stability, discriminatory strength, and effectiveness of alternatives were verified for the two tests for students. The descriptive, analytical and inferential research method was used, and three statistical hypotheses were formulated for the research, which are as follows: 1- There is a statistically significant difference at the significance level (0.05) between the hypothetical mean and the arithmetic mean of the students' scores in general in the tests of deep understanding skills. 2- There is no statistically significant difference at the level of significance (0.05) between the hypothetical mean and the arithmetic mean of the students’ scores in general in the tests of mathematical modeling skills. 3- There is no statistically significant relationship at the significance level (0.05) between the skills of deep understanding and the skills of mathematical modeling among the students of the fifth scientific grade in general. These hypotheses were tested by statistical methods (parametric and non-parametric methods) test, estimates of the effect coefficients according to the simple non-linear regression model of the cubic polynomial, Pearson's simple correlation coefficient, half-segmentation method, non-parametric Mann-Whitney test, (Ki-test). Square), and this was achieved by using the ready-made statistical package (SPSS), and the search results were as follows: 1- There is a similarity in the low level of students' responses in general in the skills of deep understanding. 2- A low level of students' responses in general to the test of mathematical modeling skills was achieved. 3- There is a correlation according to the polynomial model used between the effect of mathematical modeling skills on the dimension function of deep understanding skills for the two groups of male and female students. In light of the results of the research, the researcher recommended several recommendations, including: the inclusion of the mathematics curriculum with exercises, activities and exercises that require employing mathematical modeling skills and deep understanding skills, and working to increase the qualification and training of mathematics teachers by preparing special training courses for this purpose related to introducing them to mathematical modeling and its importance and how to implement it in the classroom , the researcher suggested several proposals, including: Conducting a study to reveal the ability of mathematics teachers on mathematical modeling skills