Objectives: Informed by a social-ecological framework, this study nested undocumented students' individual mental health needs within micro-level campus factors and the macro-level immigration policy context to examine how these are associated with undocumented Latina/o/x college students' use of on-campus mental health services. Method: A large-scale survey was administered to 1,277 undocumented college students attending 4-year public universities in California. Only Latina/o/x respondents were included in this study (N = 1,181). Fifty percent of students attended a UC system (n = 589). On average, students were 21.84 years old (SE = .15), and most were women (75.3%, n = 890). Results: Greater level of mental health symptoms and perceived mental health need, and greater use of campus-wide resources and undocumented student services predicted greater likelihood of using on-campus mental health services. Greater perceptions of social exclusion due to the immigration policy context predicted lower use of mental health services. Conclusions: Results indicate that a greater use of resources and an inclusive campus environment, as well as efforts to minimize policy-related feelings of social exclusion, may facilitate undocumented students' professional mental health help-seeking. These findings emphasize the need to take multiple and multi-level ecological factors into account when considering mental health service use, particularly in the case of undocumented immigrants and likely other structurally marginalized groups. Public Significance StatementUndocumented college students face unique challenges due to their immigration status that not only compromise their mental health but also limit with their capacity to seek help from mental health professionals. This study nested undocumented students' individual mental health within campus and immigration policy contexts to examine how these are associated with students' use of on-campus mental health services. Findings show that greater perceptions of social exclusion deter undocumented students from seeking mental health services, whereas using more general campus-wide resources and undocumented student services increased the likelihood that they would seek services. Anxiety and depression symptoms as well as perceptions of mental health need were also strongly associated with mental health service use.