This study aims to determine the effect of problem solving method based on Gil and Martinez-Torregrosa model in chemistry on the problem solving skills and on understanding the nature of science among 114 grade students. The sample consisted of (137) students of the 11" grade in one school in Dakhiliya Region. The sample was divided randomly into (67) students forming the experimental group which were taught by problem solving method following a teacher guide designed by the researcher, while (70) students forming the control group which were taught by conventional method. The study last for seven weeks with total number of (22) periods in the second semester of the academic year 2007/2008. To answer the study questions, a problem solving skills test consisted of (18) items and understanding the nature of science test consisted of (20) items were used. The validity of both tests was conducted through (12) judges, where the reliability was measured by test-retest method. The correlation coefficients were (0.91), (0.80) respectively. The results revealed that: There were statistically significant differences between the two groups with respect to problem solving skills test in favor experimental group, There were statistically significant differences between the two groups with respect to understanding the nature of science test in favor experimental group. Growth of problem solving skills in both experimental and control groups was noticed, but the rate of growing for these skills in the experimental group was greater than control group. Growth of understanding the nature of science in both experimental and control groups was noticed, but the rate of growing for the understanding in the experimental group was greater than control group. A number of recommendations and suggestions were proposed in the light of the above results, such as running seminars and workshops for teachers in how to use problem solving method in teaching, and how to create authentic problems from curriculum subjects to their students. Another recommendation is conducting more research in the area of problem solving method and relate it with other subjects, different stages and variables.