The goal of this research is to determine the effectiveness of Grammar-Translation Method on EFL adult learners. The sample of this investigation was based on 30 graduated students as a universe and a sample of 15 which represent the 50% in which 9 of them were female who represent the 60% and 6 male who represent the 40% from Impact Languages Institute. The research used random sampling process to lead this investigation. The findings of this research indicated that there is a positive Correlation between the usage of Grammar Translation Method and both female and male EFL learners. This research concluded that both female and male EFL adult learners who were taught by using Grammar Translation Method progressed notably in grammar in which they achieved great self-confidence. This study recommends that further future research be led toward this investigation to overcome problems with foreign language especially in grammar.