With the restructuring of the senior secondary education system in Hong Kong in 2009, the senior secondary curriculum was overhauled substantially by the conversion of the two-year Certificate Level and the two-year Advanced Level to a new three-year senior secondary level. This process entails changes to the contents and organization of various science subjects. This study was designed to explore, through questionnaires and interviews, the perceptions of science teachers about the design of the three science curricula, namely Physics, Chemistry, and Biology, and the challenges teachers perceived for teaching and learning these subjects in the new education context before the full implementation of the reform. The findings show that the respondents were well aware of the emphases of the new curricula. However, the respondents were likely to experience difficulty in putting rhetoric into practice due to limitations inherent to the curriculum design, increased diversity of students' ability, teachers' inertia in changing old practices, and resource constraints. (Contains 6 tables.)