Since the COVID-19 pandemic, researchers have been trying to identify which personal resources can contribute to minimizing the mental health costs in students incurred due to the restrictions that disrupted safety and predictability in their academic lives. The aim of the study was to verify if and how individual factors (resilience and positivity) and socio-environmental factors (social support and nationality) allow prediction of the level of perceived stress. University students (n = 559) from Poland, Serbia, and Italy were surveyed using the Perceived Stress Scale (PSS-10), the Brief Resilience Scale (BRS), the Positivity Scale (PS), and the Interpersonal Support Evaluation List (ISEL-12). Personal resources-positivity, resilience, and support-were found to be positively interrelated and significantly associated with stress levels. Additionally, gender and nationality differentiated stress levels. A general linear model (GLM) showed that levels of perceived stress are best explained by resilience, positivity, tangible support, and gender. The results obtained can strengthen students' awareness of personal resources and their protective role in maintaining mental health, as well as contribute to the creation of prevention-oriented educational activities. Nationality was not a significant predictor of the level of perceived stress, which highlights the universality of examined predictors among university students from different countries and suggests that interventions aimed at enhancing these resources could benefit students across different cultural contexts.