The principal concern of this study is to address the influence of Kiswahili on Giha through lexical borrowing. The study identifies lexical items borrowed from Kiswahili into Giha and the reasons for the borrowing. It also examines the phonological and morphological strategies involved in integrating the loanwords and the changes occurring in the Giha lexicon as a result of lexical borrowing from Kiswahili. This study employed both purposive and simple random sampling methods. The data were collected from three villages (Mwandiga, Gungu and Mwanga) in Kigoma Urban District in Kigoma Region through questionnaires, semi-structured interview, focussed group discussions and observation as the instruments of data collection. The data were analyzed and presented both qualitatively and quantitatively. The study was guided by two theories, namely Optimality Theory and Wave Theory. It is revealed in this study that there is heavy lexical borrowing in Giha from Kiswahili. The reasons for lexical borrowing are also identified. It is observed that there are specific phonological and morphological strategies used to accommodate loanwords. The changes observed as a result of lexical borrowing range from the vocabulary, phonology, morphology and semantics of the Giha language. Since Giha has received little attention from language researchers, further studies are recommended to investigate borrowing at wider range covering the entire region.