This study aims to analyze the effect of promotion in mediating online marketing on online purchasing decisions on Bukalapak store (Studies On The Students In The Faculty of economics and Business University of Muhammadiyah Yogyakarta). The objects of this research is the Bukalapak store. The subjects in this study were students in Universitas Muhammadiyah Yogyakarta. The number of samplesused in this study is 110 respondents. Sampling method used in this study is puposive sampling, as sampling technique and data collection technique using questionnaires. The data were processed by single, multiple linear regression using IBM SPSS Statistics 16.0 software and data analysis method used was a path analysis accompaied Sobel Test is used to test the hypotesisformulated. Result of this research indicate that the online marketing positive and significant impact on the promotin. Online marketing positive and not significant impact on the online purchase decision. Promotion positive and significant impact on the online purchase decision. Finnaly, promotion can mediate significantly online marketing on the online purchase decision.