Abstract: This study attempts to identify the interferences of L1 in L2 writing among final year Malay students taking Bachelor in Teaching English as Second Language (TESL) in a Higher Education Institute in Shah Alam, Malaysia. 73 bilingual Malay students who are in their final year of study participated in this study. Data collection tool included two instruments; 1) a questionnaire in which the participants were asked regarding their perception on the interference of their L1 in their L2 writing, as well as 2) written discourse in the form of descriptive essays. The participants were provided with a text in Malay language to be convert into the second language within 30 minutes. Then, the errors were classified into six (6) categories according to the prepared rubric to find out the impact of L1 interferences in L2 writing. The findings of this study have shown that the biggest impact of first language interference can be seen in the writing is grammar, word choice, spelling, punctuation and content, whereas no evidence of error in capitalization. Yet, the negative impact on the transfer of L1 to writing in L2 were likely committed because of the non-existence of a certain rule or concept in the L1 of the participants. Besides, students’ perceptions on the interference of L1 in L2 writing have shown that they are not aware of the inadequate knowledge of English language that may have led them to do these kinds of errors.