This study aimed to find out about the influence of viral marketing and trustworthiness toward buying interest, the influence of viral marketing to trustworthiness, and the influence of viral marketing toward buying interest that was mediated by trustworthiness. This study was associative study using primary and secondary data. Data collection tools and techniques with the questionnaire, survey, and interviews. The population within this study were students from Mataram University who use social media. Samples were obtained using accidental sampling. Data analysis used path analysis. The results of this study showed that viral marketing and trustworthiness influencing both positively and significant toward buying interest, there was the influence of viral marketing both positively and significant toward trustworthiness, and there was the influence of viral marketing both positively and significant toward buying interest with trustworthiness as the mediation variables.