Background: COVID-19 has dominated health, economic, and geopolitical issues for many months, but it also has great influence on individuals and families. The aim of this study was to verify whether the pandemic of COVID-19 changed religious practices and how religiosity moderated the influence of the pandemic on family interactions and attitudes towards health issues in adolescents. Methods: The study groups included 561 adolescent high school students (314 females and 247 males) from two kinds of high schools: public and Catholic. Results: Most Catholic school students have not changed their religious practices during the pandemic or just changed the form of attendance to TV or internet (59.7%). Moreover, 8.6% of them stopped the practices, in comparison with 12.9% of public school students, most of whom had not attended a mass before and during the pandemic. The results showed that in adolescents’ opinions the pandemic caused family relations to be stronger, however this effect was modified by religiosity. Conclusion: Attending Catholic school and being a practicing believer influenced some aspects of faith and family relations during the pandemic, but in most aspects, they did not influence attitudes toward health issues. The results of the study highlight the need to secure, especially for non-believing adolescents, family support during the pandemic, while in believers faith may provide such support.