This research was aimed at finding out the efficacy of Collect, Organize, Write (COW) Strategy in teaching argumentative essay writing to Indonesian EFL students. This research was conducted at the second semester of English education study program of IAIN Palopo, an Indonesian University. The total number of samples was 20 students. This research used a pre-experimental method with pre-test and post-test design. The pre-test was given to find out the basic ability of the students in writing and the post-test given to find out the students’ improvement in writing after giving the treatment through COW strategy. The findings showed that COW strategy is effective in teaching argumentative essay writing of Indonesian EFL students. It is supported by the result of significance test through SPSS 20 program that the P was 0.00. Therefore, it is recommended to use COW strategy in developing argumentative essay writing of Indonesian EFL students.
Keywords: Indonesian EFL students, COW strategy,