This study examined the relationship between Physics Teacher's Classroom Behaviour and Students' Academic Achievement in the South West Region of Cameroon. That is, the purpose of this study was to relate the classroom behaviour of physics teachers to students' academic achievement. The study was also guided by the following specific research objectives; to relate physics teacher's classroom management procedures to students' academic achievement, to relate physics teacher's classroom praise behaviour to students' academic achievement, to relate physics teacher's classroom caring behaviour to students' academic achievement and to relate physics teacher's classroom equity behaviour to students' academic achievement.