Social media has become the most popular activity among students in the modern world. The purpose of this research was to determine the impact of using English captions on Instagram to increase their vocabulary. A qualitative approach with a structured method was used in this research. There were seven participants, especially the 2017 PBI department, who used the Instagram application actively and there were nine interview questions. The result of the research shows that the impact of using English captions on Instagram greatly affects their vocabulary mastery. Such as grammatical improvements, getting a lot of vocabularies, and being able to socialize with strangers.