This thesis is a description of the phonology of Mositacha, a Lowland East Cushitic language of the Afro-Asiatic family, based on original field research. Mositacha is spoken by 6,000 people who live in the North Omo Zone of the Southern Nations, Nationalities, and People’s Region in Ethiopia. Very little has been written on Mositacha. With the exception of Wondwosen‘s recent grammar (2015), which identifies the consonant and vowel phonemes, notes consonant gemination and vowel length, and briefly comments on tone, there has been no systematic study on the Mositatcha phonology. This thesis offers a more comprehensive study on the phonology of Mositacha. It examines consonant and vowel phonemes, syllable structure, phonotactics, phonological processes and tone. Of particular interest are marginal consonant phonemes which may be attributed to ongoing language shift, phonemic vowel length, consonant sequences and gemination, and a description of pitch patterns in words in isolation.