The present study aims to explore critical thinking from EFL Thai students’ perspectives in collaborative writing activity. The subjects were 32 second-year English major students composing paragraph writing in the Writing II course. They were divided into three groups based on their English proficiency: advanced, intermediate, and novice, and data was collected using quantitative and qualitative approaches. The critical thinking skills questionnaire was utilized to collect quantitative data, and the results were analyzed using Mean and Standard deviation. For qualitative data, an interview was used to collect critical thinking skills practice of six students randomly selected. The quantitative results revealed that the highest critical thinking skills practice was found in analyzing (Mean=3.47, SD=1.15), followed by evaluating (Mean=3.44, SD=1.27), and creating (Mean=3.34, SD=.03), respectively. For qualitative results, it was found that the students in the high level of English proficiency group reported they practiced critical thinking by analyzing, evaluating, and creating. They produced a new sentence and a paragraph, selected the best ideas, and categorized the supporting details based on information and ideas from peers. Regarding intermediate and novice level groups, they reported identically that they frequently practiced analyzing and evaluating. Analyzing and assessing were two critical thinking abilities that were commonly utilized. They have to do with comparing and choosing content, as well as elements of arguments and supporting statements. As a result, collaborative writing appeared to promote pupils to use critical thinking skills when writing.