The use of Swahili language by secondary school students in communication clearly indicates whether there is an effect caused by the first language. This study aimed at finding out how Kikamba language affects the acquisition of standard Swahili by secondary school students in Yatta subcounty. Literature has been reviewed to offer various perspectives about the effect of language one on the acquisition of second language. The objectives of the study were; to examine how Kikamba affects proper articulation, to examine how Kikamba affects grammatical agreement in Swahili and to examine how Kikamba affects vocabulary in Swahili. The target population was secondary school students in Yatta subcounty and Kiswahili teachers. Questionnaires were used to gather information from students while interviews were used to gather information from teachers. A total of 1445 students and 30 teachers responded. Some of the findings included; some Kamba words were similar to Kiswahili words, wrong pronunciation of Swahili words, some students prefer using kikamba on their free time rather than Kiswahili, few students spoke fluent Swahili. The researcher concluded that a strategy that incorporates phonetic knowledge and cultural sensitivity , educators to implement focused teaching methods that support students comprehension, application and mastery of Swahili grammar rules, training to be conducted with emphasis on addressing semantic valuations and promoting the usage of Swahili terminologies. The researcher recommended on implementation of regular practice sessions focusing on Swahili phonemes that are challenging to kikamba speaking students, engage students in role playing activities where they can practice Swahili intonation and stress patterns, incorporate regular drills and practice exercises that focus on different aspects of verb, conjugation. This study is essential to secondary school learners and Kiswahili teachers because it illustrates how Kikamba affects Swahili acquisition as far as grammatical agreement, vocabulary acquisition in Swahili is concerned.