Critical thinking has gained much attention in many countries over the past few decades; however, there is no clear definition of what it is due to the richness in meaning of the term 'critical thinking' and the ambiguity of the word 'critical'. In spite of this, many scholars had contributed their conceptions of critical thinking, in which consists of skills and dispositional dimensions. The purpose of the current study was to investigate students conceptions of critical thinking. 480 Secondary 5 (Year 11) students in four Hong Kong secondary schools completed a questionnaire consisting of 40 descriptors of critical thinking. The quantitative data was conducted by principal component analysis (PCA). Results indicated that students conceived critical thinking as one dimension only, contrary to the two-dimensional conceptions of critical thinking from scholars. The results have important implications for teacher education as well as the successful implementation of Liberal Studies.