One of the factors that indicates success in English as Second Language (ESL) classrooms is the proficiency of students in oral communication. Though students have high positive attitude towards the use of ICT in learning English, they are still faced with the problem of lack of proficiency in English and lack of training in ICT. The study sought to determine the impact of Rosetta Stone CALL software on university students’ proficiency in English language. A pre-test was administered to a group of students before they were exposed to the CALL software which comprised five audio files with four thematic units each and one visual file that exposed participants to a variety of listening, speaking, reading and writing tasks. An observation schedule was used to monitor and investigate the students’ progress while a post-test was administered to the group in an attempt to determine differences (if any) in their pre-test and post-test scores. Data were analysed with descriptive and inferential statistical tools. Results showed that the students’ post-test scores were significantly higher than their pre-test scores: an indication of the impact of the Rosetta Stone CALL software on improving their proficiency in English language. Questionnaire responses indicated that a great majority of the students found the intervention process worthwhile, while observation revealed an increase in the students’ level of interaction and participation as they exhibited positive learning attitude towards the software. Recommendations were made on the need to adopt computer-assisted language learning in the teaching and learning of the English language in Nigeria.