The quantitative research method was applied to describe the data. The population of this research was the tenth-grade of SMAN 3 Panyabungan, which was divided into the experimental and control class and the total of the sample was 40 students. The researcher gave 20 questions about vocabulary to collect the data in pre-test and post-test and gave 10 questionnaires. T-test formula was used by the researcher to analyze the data. In this research, it was found that the mean of pre-test score in experimental class was 52 and in control class was found 55.72. Meanwhile, the mean of post-test score which found in experimental class was 80 and in control class was 68.25. It can be counted from the students’ score that t count was 3.748, whereas the t table was 2.024 for = 0.05 with the degree of freedom (df ) 38. It means that t count was higher than t table (3.748 > 2.024). So, alternative hypothesis (Ha) was accepted and null hypothesis (Ho) was rejected in this research. In an addition to this result, using Duolingo Application had significant effect as media in English teaching learning process. The researcher discovered that most students agreed that using the Duolingo application could effected their interest in the English teaching and learning process, particularly when learning vocabulary. Another instrument was used to measure students' perceptions toward using the Duolingo application. In this sense, it may be said that none of the respondents to the survey provided by the researcher expressed disagree or strongly disagree.