This study aims at finding out to what extent the skills of critical thinking are employed in the assessment activities of the curricula of "Hadith" and "Seerah" assigned for grade ten at the Institutes of Islamic Sciences. In order to achieve the aim of the study, the researcher organized a list of the main skills of critical thinking (deduction, induction and evaluation) to assess their trueness. Also, the researcher prepared a criterion to evaluate to what extent the skills of critical thinking mentioned above are included in the curricula of "Hadith" and "Seerah". This assessment was done with assistance of some specialists from SQU, Ministry of Education, Sultan Qaboos Center for Islamic Culture and the Institute of Islamic sciences. The study sample included (174) assessment activities from the curriculum of "Hadith" and (165) activities from the curriculum of "Seerah". All these activities are found in the Curricula assigned for grade ten at the Institutes of Islamic Sciences (2006-2007). Then, the found activities were analyzed in the light of the skills of critical thinking (deduction, induction and evaluation) and the head question was considered the analysis unit. The main findings the researcher came up with are as the following: - The evaluative activities of "Hadith" and "Seerah" curricula included all the skills of critical thinking (deduction, induction and evaluation) but induction came in the first position in terms of frequency, then deduction and finally evaluation. - The evaluative activities found in the curriculum of "Hadith" included = more skills of critical thinking than the activities of "Seerah" curriculum. Based on these findings, the researcher recommends that all skills of critical thinking have to be included equally according to pedagogically specified percentages.