Despite extensive research, the mental health implication of social media in adolescents is not yet understood due to mixed and inconsistent findings and more in-depth qualitative studies are needed to expand our understanding of the impact of social media on adolescent mental health during the Covid-19 pandemic. The purpose of this study was to explore why and how adolescents use social media, adolescents’ lived experiences on social media, how they make sense of these experiences having impact on their mental health, and the influence of the Covid-19 pandemic on their use of social media and mental health. In-depth interviews were conducted with eleven adolescents aged 14-16 (five female, six male) across England. The interviews were audio-recorded, transcribed verbatim and analysed using interpretative phenomenological analysis. Two key themes were identified: the beauty of social media that captured positive experiences and emotions of adolescents and the beast of social media that captured negative experiences and emotions. From the adolescents’ accounts, social media has both positive and negative impacts on their mental health, but mostly positive impacts during the Covid-19 pandemic. The results were discussed in relation to the study aims and previous study findings. Strengths and methodological limitations of the study, implications for future research that emerged from the study were discussed.