This study aims at identifying the effectiveness of the methodology of 'Problem solving' on teaching fiqh on the short-lasting learning of second secondary students and on their long-lasting learning. This study is done through answering two questions: First, "Is there any statistical differences in the immediate (short-term) between students who study with "problem solving methodology and students who study under the common methodology in learning two chapters of second secondary Fiqh subject?". Second, "Is there any statistical differences in the long-term learning between students who study with problem-solving methodology and students who learn under common methodology in learning two chapters of second secondary Fiqh subject ?". The study covers 41 students, 20 of them represent the experimental group and 21 students represent the Control group. All are students from the Islamic Sciences Institute at Muscat that belongs to the Sultan Qaboos Centre for Islamic Culture. Before the implementation of the study, the researcher ascertained, from the results of fiqh exams of the academic term before the study, that the two groups are equal. T-test exams showed that the two groups are equal. The researcher prepared a teacher's guidance book with accordance to the steps of 'Problem solving and an exam of 50 points of multiple choice was prepared. Immediately after the test, the progress of learning was measured. The test was carried out a month and a half later to measure the preservation of learning (long-term learning). The results were analyzed by T-test. The study shows that the experimental group was much better in both short term and longterm learning. Therefore the study has concluded with some recommendations. The most significant is that it is necessary to train teachers of Islamic studies (al-Tarbiyya alIslamiyya) to use modern methodologies of teaching, especially 'Problem solving' because of its great impact on the educational process. The study has also offered some suggestions. Most important of all is a suggestion to implement 'Problem Solving' methodology on other branches of (al-Tarbiyya al-Islamiyya) wherever it is suitable and applicable.