Liberal Studies will be a core subject in the new senior secondary curriculum to be implemented in 2009 in Hong Kong. The subject is very new to many pre-service and serving teachers who will be taking up teaching in this subject specialty. The present study is intended to be an exploratory one, with the aim of learning about how pre-service teachers majoring in Liberal Studies in a Postgraduate Diploma in Education programme offered by a local university make decisions when planning for lessons in the subject. The findings show that three factors played a key role in these teachers’ instructional decision making – disciplinary backgrounds, curriculum considerations, and considerations of how to represent knowledge for students. The findings will contribute to an understanding of the professional learning needs of Liberal Studies teachers.