Abstract: The purpose of the study was to investigate the effects of critical thinking skills on speaking ability among students of non-English major. The study was conducted at Dai Nam University with 74 students from three disciplines; linguistics, healthcare and technology. The research design were survey and experimental. The findings reveal that the levels of critical thinking skills vary across disciplines. Linguistics students hold the least (M=1.87). This indicates that the students were categorized as a "Basic Critical Thinker." The Healthcare students ranked the top (M=3.07). A ranking within this range (M= 3.00 to 3.99) places the individuals in the "Proficient Critical Thinker". Technology students were categorized as "Emerging Critical Thinker” (M=2.10). The aspects of Clarity of Communication and Problem Solving Skills contributed mostly to the development of speaking ability B = 0.79, t(69) = 3.51, p < .001 and B = 0.57, t(69) = 2.23, p = .005 respectively. The critical training course proved beneficial for students in terms of enhancing speaking ability; mean of post-test was significantly higher than mean of pre-test M= 6.28 and M=5.03 respectively.