University students demonstrate high rates of gambling behavior, which can have negative health consequences. Mobile gambling has rapidly expanded, and most students own a device. It is therefore important to understand the key psychological factors underlying students’ mobile gambling. This information could be used to inform interventions. Psychological determinants and beliefs were identified using the Reasoned Action Approach (RAA: Fishbein & Ajzen, 2010). Study 1 identified the modal salient behavioral, normative, and control beliefs. Thirty-five participants completed a questionnaire concerning each belief category. Content analysis identified 27 modal salient beliefs; Eleven behavioral, nine normative, and seven control. Study 2 assessed the predictive utility of the RAA and key beliefs using a cross-sectional design. Participants completed questionnaires assessing RAA determinants (N = 473) and mobile gambling behavior (N = 388). Constructs accounted for 66% and 56% of the variance in intention and behavior, respectively. Attitude (affective and instrumental) and injunctive norm significantly predicted intention, and intention and autonomy significantly predicted behavior. A number of key beliefs were identified including “Bonus offers and promotions” and “Access and availability of apps”. The studies provide important information regarding the psychology underlying students’ mobile gambling behavior. Interventions could target the identified key beliefs to change the behavior.