Introduction: critical thinking skill in health science education is considered as the ultimate goal of learning. This study aimed to determine the effect of educational workshop on improving the critical thinking skills of Nursing students.

Methods: In a quasi-experimental study with a before and after design, 32 undergraduate Nursing students from seven level of Baqiyatollah University of Medical Sciences (n=16) and Artesh University of Medical Sciences (n=16)  in 1394 with informed consent participated in the study and due to better access for intervention, the students from Baqiyatollah University of Medical Sciences put in the experimental group and the students from Artesh University of Medical Sciences put in control group. The experimental group students trained critical thinking skills in a workshop for 6 hours. Critical thinking was assessed by using a 34-item California critical thinking skills (Form B) before, immediately after and one month after education in both groups. Information obtained were analyzed by using SPSS software (version 22) and descriptive statistics and inferential statistical significant level (p<0. 05).

Results: The results showed that test critical thinking, the difference in mean total scores and scores of dimensions ( analysis , evaluation, inference , deductive reasoning and deductive reasoning ) questionnaire critical thinking in the process before, immediately after and one month follow up after training the experimental group significantly more than the control group (P<0 . 05) .

Conclusion: Increased students' scores on the total score of critical thinking skills and aspects of analysis, evaluation, inference, inductive reasoning and deductive reasoning reflects the value of the effect of educational workshop on promoting critical thinking skills and clinical decision making of students .