In Malawi, the new Biology curriculum draws from constructivist approaches. The Biology teaching syllabus emphasises the use of students’ experiences as a resource and the use of active student involvement strategies when teaching the curriculum to enhance conceptual understanding. However, inspection reports show that students are less actively involved in the lessons and the teachers rarely draw from their students’ prior experiences to enhance conceptual understanding. In this study, I investigated some factors affecting four teachers’ use of constructivist approaches when teaching the new biology curriculum in Malawi. Information was collected on the four teachers’ understandings of active student involvement in lessons and students’ experiences, the extent to which the four teachers involved students and built on students’ experiences to enable comprehension of science concepts in the Biology lessons and the factors that promoted/ hindered the use of these practices. Data was collected through lesson observations and interviews with teachers using an observation guide and an interview schedule respectively. Four Biology teachers, two from community secondary schools and two from conventional secondary schools were observed and interviewed. I found that all the four teachers understood students’ experiences as prior knowledge from previous school learning. The teachers understood active student involvement in relation to the type of schools they were teaching. For the teachers in community schools, involving students meant engaging them in group discussion while to the teachers in conventional schools it meant students doing experiments / practical work. Their teaching focused on giving information and little was done to develop students’ metacognitive abilities. According to the four teachers, pressure to cover the syllabus before the national examinations; lack of text books and laboratory equipment; lack of motivation among students; students’ backgrounds; and inadequate students’ fluency in the English language are some of the factors that affect their implementation of the constructivist approaches. Based on the lessons I observed, the teachers’ knowledge of subject matter and teachers’ understandings of the constructivism concept also affect the use of constructivist approaches when teaching Biology in Malawi.