The aim of the present study was to address the influence of Kiswahili as L1 on the acquisition of English phonology by Kiswahili native speakers learning ESL. Three specific objectives guided the study by providing evidence of cross-linguistic influence involving phonological transfer both at segmental and suprasegmental level. The study sought to determine the phonological transfer by Kiswahili learners of ESL at the levels of vowels, word stress and intonation involving interrogatives. The findings revealed that, to a large extent, native Kiswahili speakers who learn ESL transferred their five already acquired Kiswahili vowels into English. As a result, the English complex vowels were avoided by the respondents by the unconscious use of such strategies as vowel substitution, vowel epenthesis, glide epenthesis, vowel length reduction and monophthongization. Further studies are recommended to investigate the influence at a wide range covering the entire country as well as focusing on aspects of L1 transfer involving other linguistic levels such as morphology, syntax, semantics and pragmatics.