Adeniran Ogunsanya College of Education, Otto/ljanikin Lagos, Nigeria Email: adebanjowumy@gmail.comThe influence of the mother tongue on the learning of the second language cannot be over emphasized. This influence is called interference and it could be positive or negative. When it is positive, it facilitates learning, but when it is negative, it hinders the learning of the target language. A person learns a second language partly in terms of the first kinds of meanings already learnt in the first language, the first language (also called the mother tongue) thereby serves as a foundation on which the learning of the second language is based. The language learner associates words in the target language with those of his first language. The effect of a previously leant language on a language learnt latter is greater in the area of phonology, grammar and semantics. This paper looks at how the knowledge of Yoruba (a major language in the Western part of Nigeria in Africa) interferes with the learning of English languages.Keywords: Interference, mother tongue, phonology, language