The study aims to explore the use of L1 Bahasa Indonesia in the L2 English writing process specifically within the demographic of Indonesian students currently studying in U.S universities. In the second language writing field research related to L1 in L2, even though there have been studies with many Asian demographics like Chinese, Korean, and Japan. However, there seems to be little studies have been conducted with Indonesian demographics. Moreover, research within this particular topic is mostly conducted quantitatively by looking at how much L1 is used during the L2 composing process by incorporating Think-Aloud protocols. In addition to that, it can be seen that Think Aloud Protocols have also predominantly been used to investigate the issue of L1 in L2. Even though Think-Aloud as a method has been proven to be useful, it can also be argued that such a method is too intrusive for the participants. Therefore, this current study is conducted with qualitative descriptive without Think-Aloud Protocols looking at ten participants from ten different universities in the U.S. studying non-English majors. The data were gathered from questionnaires, writing tasks that occur simultaneously with writing observation, as well as stimulated recall interviews to enable triangulation. The findings from the data analysis suggest there are similar patterns that can be found on participants with some unique difference. For example, the instruction to think aloud is not given by the researcher yet some participants practiced thinking aloud naturally during their writing process. Furthermore, L1 use are found to be a complex as accessing linguistics repertoire, recalling memory or start the first sentence/paragraph. While some L1 use effects include sense making, looking for ideas and time efficiency. Therefore, each participant's interaction with their L1 and the effects of L1 use in L2 are discussed.