Abstract-This paper examines the language interference in English speaking skill. The interference was influenced by the mother tongue of the learners. Therefore, this study explains the forms of language interference in the students' speaking skill and the factors affecting the language interference. In addition, the study attempts to use case study with descriptive qualitative research approach. The data were collected by using the questionnaire and recording technique. The data, then, were analyzed based on the students 'sound production. Subsequently, The data were formulated on the table illustrating the spread of the students' interference. In identifying the students' sounds, three classifications of the English pronunciation were applied. The result shows that most of the students made error in their pronunciation, 2% of consonants and 3% of vowel. The student's sound production did many mistakes in their pronunciation started from consonants to vowel sound. The mistakes in consonant sounds caused by the mother tongue were highly interfered. The pronunciation in manner of articulation occurred in consonants such as plosive and nasal sounds. Moreover, for the place of articulation, the errors appeared on dental and palate-alveolar. The factors influencing the mother tongue interference in the students' pronunciation are the environment, students' motivation, and the language sound system.