The study aims to find out whether applying critical thinking can improve the students’ abilities in speaking skills, and to find out whether this method can enhance learners’ English competence. With the attempts to bridge the gap between theories and instructional practices through the design and implementation of a content-based Navigate B1 book, two groups of post graduate students participated in the study. A12 topic-unit syllabus, including the subject areas of language arts, science, and social studies, was designed and implemented. Data were collected via a teacher-constructed language proficiency test and an introspective interview. The findings revealed significant gains in the students’ English language proficiency test scores. A questionnaire was also given to the learners which assessed their attitudes toward learning speaking by applying critical thinking. Based on the findings of the study, it revealed that learners of the critical thinking oriented class had a fairly effective tendency and positive performance toward speaking learning process, greater than what was observed in the group with traditional teaching methods.