Night-time social media use in young people has received significant attention from the international media, governments, and policymakers due to its published associations with increased depression, anxiety, and sleep problems. However - as not all young people engage with social media in the same way - there are calls for a shift of research focus away from suggested negative impacts of social media use and towards nuanced understanding of social media engagement style. As a result, individual differences in social media engagement must be appreciated when considering the relationship between social media use and wellbeing. The current study presents pilot data which highlights an association between social comparison orientation, night-time social media use, mental wellbeing, and sleep in female users of Facebook and Instagram (N = 60). Social comparison orientation, rumination tendency, sleep health, and night-time social media use were examined using online questionnaire measures. Social comparison orientation was found to be positively associated with night-time social media use and rumination tendency. In addition, rumination was highlighted as a significant mediator of the relationship between social comparison behaviour and poor sleep – suggesting that the behaviours we engage in online may influence sleep through a cognitive pathway. Our findings contribute to a growing body of research which demonstrates how the nature of social media interactions can impact wellbeing with implications for the design of integrated social media literacy and sleep interventions.