This study analyzed the critical thinking of pre-service biology teachers in SSI argumentation writing in 'Biology logic and essay' and examined its changes. To this end, 56 of SSI argumentation writing results written by 14 pre-service biology teachers at J University's College of Education were analyzed. In addition, the critical thinking shown in these writing products were examined in seven subareas: purpose, information, concept, logic, assumption, conclusion, and perspective. As a result of the analysis of critical thinking, among the SSI argumentation writings, the average of the first writing was the lowest and the average of the third writing was the highest. In the analysis of the sub-areas of critical thinking, it was found that the purpose, logic, and conclusion domains in SSI argumentation writing generally showed high averages, while the assumptions and perspective sub-areas were relatively low. In addition, in the Kruskal-Wallis test, the critical thinking of pre-service biology teachers in SSI argumentation writing showed a significant difference according to the writing sessions. In the analysis of the sub-areas of critical thinking, significant differences were found in the areas of purpose, information, concept, logic, and perspective, but no significant differences were found in the areas of assumptions and conclusions. In the post hoc test to find out the difference between the groups, there was a significant difference in the critical thinking of pre-service biology teachers between the 2nd and 4th sessions of writing. The results of this study suggest that the critical thinking of pre-service biology teachers can be improved by strengthening the SSI argumentation writing activity in the 'Biology logic and essay' class.