Background and Objective: Development of critical thinking and practical skills has remained a serious and considerable challenge throughout the nursing educational system in Iran. Conventional methods of teaching such as lectures as the dominant method used in higher education system is a passive style which ignores critical thinking. Therefore, the aim of this study was to compare the effect of instruction by Concept-Mapping and conventional Method on critical thinking skills of nursing students. Materials and Methods:This quasi-experimental study was carried out on 70 nursing students of Tehran Nursing and Midwifery schoolwho were selected through convenient sampling method, then were divided randomly into the two equal Experimental and Control groups. Educational content was presented in the form of Concept-Mapping in the Experimental group and Lecture,Demonstration and Practicalexercises in the control group. Data collection included a demographic information and California Critical Thinking Skills (form B) questionnairewhich was completed at the beginning and at the end of the fourth week of Instructional period. Data were analyzed using SPSS software (V: 21), descriptive and analytical Statistics; at the significant level P<0.05. Results: Before the intervention, the mean of critical thinking skill score was 9.71±2.66 in concept mapping group and 9.64 ± 2.14 in conventional group and the difference was not significant (P=0.121), but after the intervention, a significant difference was found between the intervention and conventionalgroup (15.20±2.71 vs 10.25±2.06, P=0.003). Conclusion: Using Concept mapping strategy in the education of nursing students may lead to developing critical thinking skills as one of the important missions of higher education. So it is recommended to usethis method in clinical nursing education.