Purpose: The main purpose of this study is to analyze the impact of the Quizlet application, a computer-aided vocabulary learning tool widely recognized as an online flashcard application, on the development and retention of English vocabulary among students learning English as a foreign language. Design/Methodology/Approach: The data were obtained from 34 fifth-grade students studying English as a foreign language during 2019-2020 academic year at Yediiklim Secondary School in Karesi district of Balıkesir province. The research was conducted using a quantitative research method within quasi-experimental design without pre-test post-test control group. Quantitative data was collected through pre and post vocabulary achievement tests, retention test and scale. While word tests aim to measure students’ vocabulary acquisition, the retention test aims to measure students’ retention of vocabulary. The Quizlet Attitude Scale was also used to obtain opinions about Quizlet. Quantitative data were analyzed statistically in SPSS Statistics. Findings: As a result of the analysis, the findings show that there is a significant difference between Quizlet and test scores. According to the results of the survey, it is concluded that the students developed positive perceptions about the use of the Quizlet program. Highlights: In the light of these findings, it is recommended to use computer-based vocabulary learning tools as a student-centered and effective teaching technique in foreign language teaching and to expand their use.