This study was conducted to explore how English language as a medium of instruction impacts students’ learning in ward secondary school in Musoma Municipal.The study employed mixed research approach whereby both qualitative and quantitative methods were used in the study. The study employed 375 respondents who were heads of schools, teachers and students in ward secondary school. Simple random sampling, stratified sampling, purposive sampling and convenient sampling technique were employed to obtain respondents. Quantitative data was collected through questionnaires and analyzed using Statistical Package for Social Science (SPSS). Qualitative data was collected through interview and observation methods. Content analysis technique was employed to analyze qualitative data. A pilot study was conducted before the research in order to examine the reliability and validity of the research instruments. Study findings were presented in form of tables, graphs and charts. The study established that most of the students have low masterly of language of instruction which hinder learning in the classroom. The study recommends that the government through Ministry of Education should change the language of instruction in primary school from Kiswahili to English so that when students reach secondary school can be able to use instruction language properly.