Although concept maps have been used to improve students' critical thinking skills, very few studies have examined the relationship between concept maps and critical thinking skills. Without this information, researchers cannot provide teachers with comprehensive suggestions for the design of concept mapping activities to improve students' critical thinking. This study aimed to examine the relationships between concept maps and critical thinking skills and explore how concept maps may differentiate individuals with low critical thinking skills from those with high critical thinking skills. A total of 70 participants were recruited from the English department of a high school in Taiwan. This study adopted a mixed-method approach. The quantitative data included students' concept map scores and critical thinking survey scores, and the qualitative data included students' concept maps. The results indicated a low Pearson correlation between the Novak and critical thinking survey scores as well as between the Gowin and critical thinking survey scores. The example scores of the concept map were the only element in Novak and Gowin's rubric that were correlated to the critical thinking survey scores. The qualitative analysis of the students' concept maps also revealed that the major difference between individuals with low critical thinking skills and those with high critical thinking skills was related to the use of examples within the concept maps.