Cantonese is the common dialect in Hong Kong. Given the increasing demand of Putonghua learning pertinent to the reunification of Hong Kong with Mainland China, Putonghua teaching has been included in primary and secondary curricula. Studies from the West have revealed that there have been a variety of sources shaping teacher beliefs. Few studies, however, have explored the critical factors that shape teaching beliefs and teaching behaviours. Case studies had been employed, with the aim to fill the gap, by exploring the life histories of four Putonghua teachers in Hong Kong with different educational and cultural backgrounds. They had been purposefully selected and allocated into two different groups for comparison, i.e. Two Cantonese speakers who were born and grew up in Hong Kong versus two non-Cantonese speakers who were born and grew up in the Mainland. Data were collected from the teachers using interviews and observations, supplemented with documentary analysis. The findings showed that the specific language learning experience exerts greater influence on teaching beliefs which in turn affect teaching behaviours. This paper also highlighted that some controversial issues over Putonghua teaching were closely related to teaching beliefs.