Background: A mediation model was proposed to explain how religiosity, religious coping, and fear of coronavirus disease 2019 (COVID-19) explained anxiety and depression among older adults. Methods: With the use of a cross-sectional design, the Integrated Health System was used to randomly invite 1000 older adults residing in Qazvin to participate in an online survey. Within the period of November 2020 to January 2021, 696 older Iranian adults (mean age=69.56years; 57.9% women) agreed to participate in the study and reported demographic information as well as measures of religiosity, fear of COVID-19, religious coping, anxiety, and depression. Results: Religiosity had direct effects on depression (B [SE]=-0.087 [0.037]; P=0.023) but not anxiety (B [SE]=-0.063 [0.036]; P=0.072). Moreover, both fear of COVID-19 and religious coping significantly mediated the association between religiosity and anxiety (B [SE]=-0.360[0.035]; p=0.002) and that between religiosity and depression (B [SE]=-0.365 [0.034];P=0.002). Conclusion: During the tough time of COVID-19 pandemic, religiosity and religious coping were protectors for older adults in developing good mental. Therefore, future research is needed to examine education programs that are effective for older adults to obtain correct knowledge concerning COVID-19, including the protective COVID-19 infection behaviors. Therefore, older adults may reduce their fear via their enhanced correct knowledge concerning COVID-19.