This study examined language use of the exogamous families in Southwestern Nigeria in order to find out the language choice in a range of domains (formal and non-formal) and with different speech partners. The theoretical framework adopted for this study is Fishman’s (1972) Domain Analysis. Language use questionnaire was structured and administered to these families. The population of the study included nine hundred (900) respondents drawn from twelve (12) Local Governments of South-western Nigeria and the respondents were strictly from exogamous families. Data collected were analysed using statistical tool. The findings revealed that English language is the most used language among the exogamous marriage families in South-Western Nigeria in both formal and non-formal domains. The study also revealed that the children of all the exogamous marriage families have language socialization as they acquired at least one of the languages spoken by their parents easily, but lack the use of it in everyday dialogue rather they prefer to use English. This is because, they lack balance bilingualism or 'multilingualism. The researchers recommended that comparable research could be conducted on exogamous couples living in both rural and urban communities in order to enrich the knowledge of the sociolinguistic findings and better assessment.