The present study aimed at developing EFL writing skill using Word Office 365 as an online collaborative learning application. The study followed the one-group pre-posttest design. The participants of the study (n=30) were EFL freshmen students enrolled in the English section at Benha university at the Faculty of Education. The instrument and materials of the present study were EFL writing skill checklist, an EFL writing skill test (a pre &post equivalent form), a rubric to score the test, and a teacher's guide for using Word Office 365. A pretest was administered to the study group to determine their levels within EFL writing skills. Then, the post- test was re-administered to the study group after using Word Office 365. Paired sample t- test was conducted to compare the means of the students’ scores on the pre-posttest. The results revealed that there is a statistically significance difference between the mean score of the study participants in the pre-and post-administration of the EFL writing skills in favor of the post administration. Therefore, it can be concluded that using Word Office 365 is effective for developing the EFL writing skill.