The use of mother tongue (MT) in EFL classrooms has been a controversial topic among researchers and teachers. While some claim that MT should not be used in EFL classrooms, others argue that MT can contribute to English language learning. The present study was conducted to investigate the use of Arabic as a mother tongue in EFL grammar classroom in the Centre for Languages at Ibb University in Yemen with a view to identifying when EFL learners favour the use of MT and the impact of that on learners and their English learning. Data were collected from EFL intermediate learners through a questionnaire administered to (51) learners and focus group discussions in which 22 learners participated. The collected data were analysed quantitatively using descriptive statistics and inferential statistics (t-test) and qualitatively. The findings showed that although the EFL learners favoured English as a medium of instruction, they showed positive attitudes towards a judicious use of their MT for some functions. Regarding the impact of MT use, the findings revealed that the EFL learners believe that the use of their MT in EFL grammar classroom is necessary due to the vital role that it can play in facilitating and enhancing their language learning as well as their cognitive ability. Statistically significant differences were not found in the mean scores of responses according to gender. Based on the findings, some recommendations to be considered to ensure effective use of MT in EFL classroom and suggestions for further research were given.