Dissertation (MA Education)The major aim of this study was to find out Tanzanian teachers’ perceptions on the use of english as medium of instruction (MOI) in secondary schools. The study found out how teachers’ understand the issues related to MOI; teachers’ perceptions on using english as a MOI; and teachers’ suggestions about the solutions to the problems of MOI. The study was guided by phenomenography theory developed by Ference Marton 1981.The study employed phenomenographic study design. This study design was chosen because the study needed small sample with in-depth understanding of the phenomenon. Data for the study were collected through interviews and focus group discussions and analysed using thematic analysis method. The study involved 5 heads of schools, 5 academic coordinators, 5 english subject teachers, 5 science subject teachers and 5 arts subject teachers. Findings from the study revealed that most teachers liked english to remain as a MOI and the reasons included: english is an international language; the language used in international business; and the language which has enough vocabulary and terminologies. Few liked the shift from english to kiswahili because teachers have low proficiency in english and students have negative attitude towards english. Based on these findings, the Ministry of Education and Vocational Training is advised to provide continuous in-service training on English proficiency. This can be accomplished through initiating refresher courses, workshops and seminars to enable teachers to master the language.