This paper intends to find out the source of language variation among Chagga people. The study was guided by four specific objectives which were: to investigate the extent to which language variation exists among the Chagga, to examine the areas (aspects) which mark language variation among the Chagga, to find out the source of language variation among the Chagga, and to determine whether Chagga varieties constitute different languages or varieties (dialects) of the same language. In this study, three techniques were used to collect the primary data, which were sociolinguistic interview (free conversation), reading passage, and the wordlist. Results show that, despite the difficulties that Chagga people experience in communicating through their mother tongue, they understand each other. Their differences in speaking are based on some of the lexicon (vocabulary). Further, the study propounded the following as the reasons as to why Chagga people seem to differ in some vocabulary: geographical location, differences in origin, lack of common socialization, the existence of hostility among them as well as political unrest and the Mangi rule.