This study entitled “Students’ English Language Acquisition and their Proficiency Improvement at IPRC Kigali, Rwanda”, was carried out to evaluate the effect of students’ English language acquisition on their proficiency improvement at IPRC Kigali, Rwanda. It had three (3) specific objectives which were to: assess strategies used for teaching English Language at IPRC Kigali, identify ways in which IPRC Kigali students use to learn English as a language of instruction, as well as identifying factors affecting English acquisition as the second language at IPRC Kigali. The methodology that was used in data collection is descriptive survey. Purposive and stratified random were used as sampling techniques. Questionnaires were used as data collection instruments. The sample size was determined by Slovin’s Formula as the population size is definite. 153 students were selected to answer to research questions. 93 of them responded and returned questionnaires. The data collected was analyzed using SPSS software. The study came up with the following findings: The mostly used strategies for the English Language Acquisition at IPRC Kigali include lecturers creating the learner-centered classroom to set students’ learning responsibilities (79.6%), and building in students’ motivation including value, self-efficacy and attributions (75.2%). The most ways in which IPRC Kigali students use to Learn English as a language of instruction include imitation (100%), repetition and practice to pronounce words and memorize them (100) conversations and discussions with colleagues and lecturers (76.4%), using English in different situations like in meetings, in shopping malls, ... and other extra-curricular activities (75.2%). It has also been revealed that age (76.3%), attitude towards English (67.8%), motivation (100%), first language proficiency (89.3%), technology (100%), and Intellectual capacity (86.0%) affect the Acquisition of English as a Second Language. It has been recommended that It is of paramount importance to enhance teaching of English as a subject but also keeping in mind that this is a Medium of Instruction in Rwanda. Lecturers should interlink this philosophy with methodologies and strategies that allow students to take lead in the teaching and learning process. Lecturers should consider the students’ individual differences to help them improve individually. Drama and play should also be integrated in teaching and learning/acquisition of English to improve students’ speaking skills through performance.