Recently, the use of social media has penetrated many aspects of our daily lives. Therefore, it has stimulated much debate and polarisation regarding its impact on mental well-being. The present study investigated the association between problematic use of social media, subjective well-being, and insomnia's potential mediator. A proportionate random sample was collected from a Univerity in Algeria between March and April 2020.The participants (n=288; mean [SD] age = 20.83 [2.13]) involved 101 (35.1%) males. Nearly three-fourths of the participants (n=214; 74.3%) used up more-than three hours daily surfing on social media. Their mean (SD) score was 15.64 (4.80) on the Bergan Social Media Addiction Scale, 16.19 (9.15) on the Arabic Scale of Insomnia, and 28.13 (7.90) on the overall subjective well-being. Structural equation modeling (SEM) revealed an indirect correlation between problematic use of social media and the overall subjective well-being of users. Similarly, the indirect but not direct effects were found for the overall subjective well-being subdomains. Moreover, all SEM models have a satisfactory fit with the data. Based on the results, it can be concluded that insomnia appears to play an important role in mediating the association between subjective well-being and problematic social media use. This suggests the importance of tackling the issues of insomnia and problematic use of social media for university students. It also has important implications in dealing with the misuse of social media, especially during the covid-19 pandemic.