3 1Department of Psychology, Jeffrey Cheah School of Medicine and Health Sciences, Monash University Malaysia, Subang Jaya, Malaysia 2South East Asia Community Observatory, Jeffrey Cheah School of Medicine and Health Sciences, Monash University Malaysia, Segamat, Malaysia 3Sunway Medical Centre, Subang Jaya, Malaysia Many psychological researchers have proven the deteriorating effects of the coronavirus disease 2019 (Covid-19) pandemic on public mental health. In Malaysia, various Covid-19 clusters were associated with religious gatherings. From a cultural psychology perspective, how ethno-religious groups respond to this crisis originating from their unique rationality and ecological systems. Therefore, this study aimed to explore the illness perceptions of major religious groups (Christian, Muslim, and Buddhist) in Malaysia toward the Covid-19 pandemic, their stress levels, and the relationship between illness perception, stress, and forms of religious expression during the lockdown period. Through an online survey method, 608 Malaysian religious believers were included in this mixed-method empirical study, which adapted standardized instruments [Duke University Religion Index (DUREL), Brief Illness Perception Questionnaire (BIPQ), and Perceived Stress Scale (PSS)]. Statistical analysis showed that all three groups reported moderate levels of stress in average without any significant difference after controlling for age. Both internal and external forms of religious expression had a significant negative relationship with stress levels. Personal control, comprehension, and emotions domains of illness perception accounted for a significant variance in the stress level. Furthermore, religious expression significantly moderated the relationship between some illness perception domains and stress. Qualitative coding revealed that most participants perceived human behavior and attitudes, sociopolitical, and sociological factors as causal factors to the current pandemic. These findings confirmed the relationship between religious expression, illness belief, and stress regulation during the pandemic lockdown. Incidental findings of age as a potential protective factor for Malaysian believers warrants further study. In the conclusion, implications for public health policymakers and religious communities on pandemic prevention and well-being promotion were discussed.