Given the rapid growth of social media, it is important to understand the impacts of social media marketing strategy on consumers’ purchase decisions in the e-commerce environment, especially, in developing country like Indonesia. Some companies have linked themselves to social media to enhance user interactions. Along with users that are increasing time spent on social media, which will influence their purchase decision. mThis study is focusing on the customers' perspective centered not only on the exposure of social media marketing, but also on their purchase decision on Grab-company in Medan. This study is quantitative research and online questionnaires were distributed to 102 respondents who are social media users in order to obtain necessary data and to test the hypothesis based on survey data collected.The results demonstrate how social media marketing strategies have positive and significantly moderate relationship towards customer purchase decision of Medan’s customer on Grab. One perspective on social media, the result suggests that users have grown dramatically across all age groups. It is also found that either owning vehicle or not is considered not a determinant factor in choosing Grab as transport.The findings in this research reached certain conclusions for both theory and practice. According to the gaps detected by the study's results, the writer provides suggestions not only for Grab’s company, but also suggestion for the further research.