Quarantine plays a key role in controlling the pandemic of 2019 coronavirus disease (COVID-19). This study investigated (a) the associations between mandatory quarantine status and negative cognitions (perceived discrimination because of COVID-19 and perceived risk of COVID-19 infection)/mental health status (emotional distress because of COVID-19, probable depression, and self-harm/suicidal ideation), (b) the associations between the negative cognitions and mental health status, and (c) potential mediations between quarantined status and probable depression and self-harm/suicidal ideation via COVID-19-related negative cognitions/emotional distress. An online cross-sectional survey was conducted among 24,378 students of 26 universities in 16 Chinese cities (February 1-10, 2020). Correlation coefficients, odds ratios (OR), structural equation modeling, and other statistics were used for data analysis. Mandatory quarantined status was significantly and positively associated with perceived discrimination (Cohen's d = 0.62), perceived high/very high risk of infection (OR = 1.61), emotional distress (Cohen's d = 0.46), probable depression (OR = 2.54), and self-harm/suicidal ideation (OR = 4.98). Perceived discrimination was moderately and positively associated with emotional distress (Spearman correlation = 0.44). Associations between perceived risk of infection and mental health variables were significant but relatively weak. Cross-sectional mediation models showed good model fit, but the overall indirect paths via COVID-19-related negative cognitions/emotional distress only accounted for 12-15% of the total effects between quarantined status and probable depression and self-harm/suicidal ideation. In conclusion, quarantined participants were more likely than others to perceive discrimination and exhibit mental distress. It is important to integrate mental health care into the planning and implementation of quarantine measures. Future longitudinal studies to explore mechanisms underlying the mental health impact of quarantines are warranted. (PsycInfo Database Record (c) 2020 APA, all rights reserved).