This study investigated the effect of using the l1 for teaching grammar in the english as a foreign language (efl) classroom at an ecuadorian university. To date, research has focused on the teachers and students’ beliefs and preferences about first language use, its distribution during class time, its functions while learners perform tasks collaboratively and on the interactions between teacher and students in class. There have been a few recent studies on the effects of the l1 on l2 learning, but these have focused on vocabulary learning. in the present study, seventy-one students enrolled in a pre-university course, ages 17-36 years old, were randomly allocated to an l1 grammar teaching condition or to an english-only grammar teaching condition, and their performance on grammar tests was compared. The findings of this study indicate that both the l1 condition and the l2-only condition had a positive effect on grammar learning.