This experimental study endeavored to assess the impact of L1 use in pre-writing (ideagenerating) stage on L2 writing. The participants of the study were grade 11 students in Belay Zeleke Preparatory School, Bichena. A comparison between the participants’ (control and experimental groups) pre-and post-writing test’ results was made. T-test was employed as statistical tool of analyses. Besides, interviews were conducted to see participants’ reflections concerning the use of L1 during the idea-generating stage. The latter was analyzed qualitatively. The results of the study showed that the experimental group significantly exceeded the control group due to the post-test content results. The interview result unveiled that the majority of the participants had preferred to use their L1 for discussing ideas at a pre-writing stage of L2 writing. Finally, it was concluded that L1 use at pre-writing stage helps participants produce better content during their writing in an L2. On the basis of the findings and the conclusions made, a judicious and cautious employment of the L1 during the idea-generating stage in L2 writing was suggested as a pedagogical implication.