The aims of the research were to examine the effect of Hello English application on students’ English vocabulary development at the seven-grade level of SMP PGRI Selapajang Jaya in academic year 2020/2021 and to know the perceptions of students on utilizing the Hello English App to increase English words. This study applied a quantitative method with quasi-experimental design. The seventh-grade students of SMP PGRI Selapajang Jaya in the academic year 2020/2021 was used as the population; also, the research sample was both classes consisting of 30 students in each class (experimental and control). The researcher provided a multiple-choice test as the instrument. The researcher employed statistical calculating of the t-test formula with 5% significance level utilizing SPSS 22 version. In accordance with the research findings, it discovered the mean score of a post-test in the treatment class was higher than the conventional class (76.67 > 62.50). The result of t-test showed that t0 (4.184) was higher than ttable (2.003); thus, it indicates that Ha is acceptable while Ho is rejectable, and it is concluded that utilizing Hello English has a significance impact on the development of students’ English words at the seventh-grade level of SMP PGRI Selapajang Jaya in academic year 2020/2021. Questionnaire was also applied as another research instrument to measure students’ perception in learning English words employing the Hello English application. As recorded by the questionnaire results, the students agree that the Hello English App can assist them in English learning, particularly English words; also, they felt satisfied and loved the learning process when they employed the Hello English App to acquire English words.