The purpose of this study is to investigate family factors in relation to young Chinese immigrants' code-switching and language maintenance. Specific attention is given to children's code-switching behaviour and how parents respond and the effect of parental response upon children's language choice in any subsequent utterance. Attempts are also made to identify the family factors that might have an effect on making language choice. Data were collected monthly through naturalistic tape-recording of families' conversations for one calendar year. Recordings of every other month were transcribed and coded for analysis. A questionnaire was used with the children's parents to obtain general family background information as well as to compare the parents' language beliefs and their actual language behaviour in real life.Results indicated that within an average of 28.1 months of stay in New Zealand, the use of Mandarin Chinese, their ethnic language, was dramatically reduced. In typical family conversations, the parents were using Mandarin Chinese in only 75.6% of their conversational turns and that figure for the children was 65.1%. If the amount of mother tongue use at home is an indicator, then the speed of shift in these families investigated appears to be relatively fast. Few parents, however, felt that their children were using too much English or ever attempted to stop them doing this, despite the fact that all the parents claimed that they very much wanted their children to maintain the ethnic language and were fully aware of the importance of their role as the main input source of their ethnic language. This seems to suggest that the marketplace value of the mainstream language is overtaking the core value of their ethnic language.Results also showed that parental use of English caused a substantially increased use of English from their children. There tended to be an "upgrading" towards English in the children's language choice suggesting that code-switching could be a temporary stage for the children along the gradual process of language shift. On the other hand, the parents were also found using more English after their children's code-switching. One of the reasons for this might be that the parents want to improve their English and regard their children as an ideal person to practise English with.With regard to daily communication functions, results showed that children often resorted to English for daily speech acts indicating that language function replacement has occurred for many daily communicative functions resulting from a gradually reduced use of the ethnic language.Many family factors were found to be affecting language use in the families: the presence of grandparents and the decision to return to their birth country for residence in the future were clearly correlated with increased use of the ethnic language; the parents' level of English language, on the other hand, was found to be related to the amount of English used, though with exceptions.These results strongly suggest that English is taking over the family domains that used to belong to the ethnic language. Parents who want their children to maintain their ethnic language need to put daily effort into action. Without painstaking daily effort, language shift will and probably is happening no matter how strong their theoretical beliefs might be.