This paper examined the effectiveness of Twitter to enhance the students' vocabulary achievement, because vocabulary is considered to have an important role in increasing students' academic achievement and skills. It employed a quasi-experimental design and involved 64 students which divided into control and experimental group. The findings of the research discovered that both of group increased their achievement; however the students in experimental group get higher score than control group. The students in the control group were categorized as students with “good” achievement, while the students in the experimental were students with “very good” achievement.