The main Objective of this study was to recognize the effect of teaching by using Inquiry method in developing the skills for evaluation of information sources authenticity for second secondary Arts students and their attitudes towards the History Subject". The problem of the study was limited to the two following questions: (1) What is the effect of teaching the unit (Crusades Wars) by using Inquiry method in developing the skills for evaluation of information sources authenticity (A critical thinking skill) for second secondary Arts students? (2) What is the effect of teaching unit (Crusades War) by using Inquiry method in developing the attitudes towards History Subject for the second secondary Arts students ? As a result of such questions, the two following hypotheses were raised. 1) There are statistically significant differences at level (a = 0.05) between the mean average in the grades of the exams of skills for evaluation of information sources authenticity (A critical thinking skill) for second secondary Arts students who studied the unit (Crusade Wars) by Inquiry method (Experimental Group) and the mean average for their colleagues who studied the same Unit by the usual method (Control group) in favor of the control group. 2) There are nostatistically significant differences at level (a = 0.05) between the mean average in the grades of the exams of skills for evaluation of information sources authenticity (A critical thinking skill) for second secondary Arts students who studied the unit (Crusade Wars) by Inquiry method (Experimental Group) and the mean average for their colleagues attitudes towards History subject and who studied the same Unit by the usual method (Control group). The population of the study was consisted of all male students in second secondary Arts class for the year 97/1998 in Eastern Region (South), totaled 401 students, might have limited the sample to two study divisions for the second secondary Art from two different schools that were randomly selected. It was divided into two groups: Experimental Group which studied the selected unit by using Inquiry method, and control group which studied the same unit by using the usual method. To answer the study questions, the researcher did the followings: 1) Re-format the (Crusades Wars) Unit from the History Book for second secondary Arts class by using the Inquiry method, then teaching it to the experimental group. 2) Develop an exam which measured the skills for evaluation of the authenticity of historical information resources, composed of 25 paragraphs in order to determine whether such sources are documented or not through exam instruction, by writing infect of every question letter A if He agreed or letter D if he disagreed. Then he mentioned the reason for his decision. The Researcher had in mind that all historical sources should be extracted from the content meaning of )Crusades) unit to facilitate the student to recognize the sources and criticize them. The exam was applied on both groups before and after the experiment. 3) Adapt a Measurement of attitudes was prepared by Dr. Faud Abu Hatab to measure students attitudes towards study subjects. It was applied on both groups before and after the experiment. To answer the study questions, the researcher used the "T-Tesť. The results of statistical analysis proved the followings: (1) The experimental group students excelled over the control groups students in the dimensional exam for the skill of evaluating the authenticity of historical information resources. In essence, we accept the first hypothesis. (2) There was Equivalence in both the experimental and the controlling group in the dimensional application for measuring attitudes towards the study subjects. In essence, we accept the second hypothesis of the study. The study recommended that history teachers should be trained on preparing and using inquiry method. Several research studies should conducted especially that measure the relationship between using inquiry method and the historical research skills.