English as an official language, has come in contact with indigenous languages in Kenya. English has therefore become one of the major donors of loanwords to these indigenous languages, Lukabaras being one of the beneficiaries. This study investigated the morpho-phonological constraints that English loan verbs encounter when adapting into Lukabaras. The research utilized Lukabaras native speakers as respondents to elicit data. A purposive sampling technique was employed to select a sample of 15 English loan verbs, which were then analyzed descriptively based on the tenets of Optimality Theory which states that constraints are universal and are fixed in their ranking and apply to all languages. The loan verbs were transcribed, and the study first analyzed the morphological constraints, followed by the phonological constraints. The findings reveal that English and Lukabaras have different morphological and phonological structures, leading to modifications of English loan verbs to fit the morphological and phonological patterns of Lukabaras. Additionally, the study identifies specific morpho-phonological constraints affecting the adaptation of English loan verbs into Lukabaras, including NOCODA, COMPLEX C, MAX IO, ONSET, DEP IO, IDENT IO, DEP-PREF, DEP-SUFFIX, and ALIGN left edge. Furthermore, faithful constraints are ranked higher than markedness constraints in Lukabaras. The study’s findings contribute to the understanding of morpho-phonological adaptation processes in language contact scenarios. Overall, the study’s findings align with the theoretical framework provided by OT, illustrating how languages manage the integration of foreign elements through a balance of faithfulness and markedness constraints. These findings not only enhance the understanding of loanword adaptation in Lukabaras but also contribute to the broader field of language contact and borrowing, providing a detailed case study of how specific constraints operate in a real-world linguistic context.