Abstract: Present opinions on the significance of mother tongue emphasize that it has a fruitful part in the teaching/ processes and if it maintained and backed in the educational settings, it would have learners experience less difficulty in learning and comprehending of different subjects. This study is an investigation on the significance of education in mother tongue in the growth of writing skill on Iranian EFL learners. The researcher conducted the investigation with 40 male and female intermediate EFL learners in (East Azerbaijan-Tabriz). After providing a valid test through a pilot study and checking its validity by CELT test, the researcher administered a proficiency test to the participants to assign them to control and experimental groups. The researcher taught the same grammar structures to the both groups. The considered grammar structures were taught to the experimental group both in English and their mother tongue, though. At the end of the course both groups were examined. The outcome of the independent sample t-test displayed that experimental group did significantly better than the control group. The conclusion emphasizes the need of education in mother tongue to have a growth in better comprehending, to facilitate and to make better teaching/learning situations.