A wide range of studies have examined the impact of collaborative learning (CL) on critical thinking skills in various learning subjects. However, very few of them are conducted in the field of Islamic education. Thus, the current study aimed at examining the impact of CL on learners' critical thinking skills in addressing Islamic radicalism as well as their critical thinking retention. Subsequently, this study also investigated learners' perspectives on CL. A mixed method approach was applied. 40 learners, 18 male and 22 female learners, from an Islamic education department at a university in Bengkulu, Indonesia, were engaged as the samples of experimentation, and 9 of them were purposively selected to be the participants for the purpose of a qualitative investigation. The quantitative data were analyzed using paired sample t-test and independent sample t-test, and the qualitative data were analyzed using an interactive model of analysis. The findings revealed that CL had a positive and significant impact on learners' critical thinking skills. CL also supported the retention of their critical thinking skills. Subsequently, the learners perceived that CL was contributive to their emotional awareness, learning motivation, cognitive development, and broad-mindedness. Grounded in the current findings, further studies can proceed to construct a theoretical CL model which incorporates components such as critical thinking, learning motivation, cognitive development, and social competence.