Computer Assisted Learning (CALL) is defined as the process in which a learner improves language skills by using a computer. Hani (2014) argued that CALL enables individualized, continuous, and authentic activities to teach and integrate the four language skills and indicates that immediate feedback can be given. Thus, this research aims to investigate and analyze the use of Twitter to improve writing skills on senior high school students and to determine its effectiveness as a tool in EAP instruction. The participants were 19 students from the senior level and an English teacher. To conduct this research, a mixed-method design was applied; and a survey and pre-post tests were administered to the participants. At the end of the research process, the participants outperformed on post-testing of writing, therefore, it can be concluded that Twitter is an effective tool to improve the written production of senior high school students, and this micro-blogging platform can be integrated to enhance EAP instruction within EFL contexts.