The term critical thinking has received much attention over the past few decades in both Western and Eastern countries and regions. From 1990s onwards, the Hong Kong educational authority undertook a series of educational reforms in order to encourage a new generation in critical thinking. In the New Senior Secondary curriculum – which commenced in 2009 - Liberal Studies is one of the core subjects in which the aim is to promote critical thinking among senior high school students. Despite this intention, there is no clear definition of what critical thinking is. The purpose of this study was to investigate teacher and student conceptions of critical thinking in Liberal Studies; and the relationship between these two conceptions. Fourteen teachers teaching Form 5 (Year 11) Liberal Studies in four secondary schools in Hong Kong, along with their 480 Secondary 5 students, completed a questionnaire consisting of 40 definers of critical thinking, and one teacher and eight students from each school participated in interviews. The results indicated that both teachers and students emphasised the skills dimension of critical thinking; and explicit and implicit relationships between teacher and student conceptions of critical thinking were found. The results have important implications for teacher education, as well as the successful implementation of Liberal Studies as a subject in the Senior Secondary Curriculum. All rights reserved.