The present study is an attempt to investigate the effect of using first language (L1) and inverse translation (IT) on the EFL students' performance in terms of specific grammatical structures (modal verbs), as well as the learners’ attitudes towards using L1 and IT in an EFL class. The mixed method design encapsulating quasi-experimental and survey study was employed. In order to triangulate the survey results, a semi-structured interview was also conducted. Sixty beginner language learners were selected as the participants based on availability sampling and assigned into the experimental and control groups. The participants of both groups took the pretest of the intended modal verbs. Then, both groups went through 12 sessions of one-hour instruction focusing on teaching modal verbs. Using IT and L1 in the control group was prohibited whereas the experimental group was taught drawing on IT and L1. Following the treatment, the participants of both groups were given a post-test on the modal verbs. The participants of the experimental group were also given a questionnaire to uncover the learners’ attitudes towards using L1 and IT in the EFL class. Finally, 5 participants of the experimental group were interviewed to answer 5 questions regarding the use of L1 and IT in the EFL class. Using descriptive and inferential statistics including the paired-sample t-tests and the ANCOVA test, the data were analyzed. The principles of grounded theory (GT) were also applied to analyze the interviews. The results suggest that using L1 and IT in teaching modal verbs has a significant effect on the participants’ performance on the post-test. The analysis of the questionnaire and the interviews also indicated participants’ positive attitudes toward using L1 and IT in the EFL class.