The number of social media users has drastically increased in recent years. Past research has focused largely on how social media use frequency and social media addiction are associated with mental and sleep health, yet fewer studies have investigated how one's perceived experiences on social media are associated with mental and sleep health. Investigating these associations among Hispanic emerging adults is crucial given that Hispanic groups may experience sleep disparities, and emerging adults are at risk of developing a mental illness. The present study investigated how online social support and online social negativity are associated with mental and sleep health among Hispanic emerging adults. Hispanic emerging adults (n = 424) completed an online cross-sectional survey assessing: sociodemographics, online social support, online social negativity, depressive, anxiety, and stress symptoms, and sleep quality. Structural equation modeling demonstrated that online social support was not associated with depressive, anxiety, or stress symptoms, nor sleep quality. However, greater online social negativity was associated with greater levels of depressive, anxiety, and stress symptoms as well as poor sleep quality. The clinical implications of these results are discussed. Prospective studies are warranted to determine the temporality of these observed associations.