Stress makes people more susceptible to various diseases. Nervous tensions affect immune system function, increase stress hormones, and weaken the immune system. The body's defense system will not be able to function properly if stress hormones are constantly produced in large quantities. In this way, the ground is prepared for various infections and diseases and the internal organs of the body will be under severe pressure. Some of the characteristics of psychological resistance or resilience to life stressors include personality traits, happiness, and humor. This narrative review study was conducted to investigate the effect of happiness and humor on improving immune system function. The papers concerning this review study were searched in SCOPUS, Pubmed, Web of Science, MedLine (Ovid), PsychINFO (Ovid), Google Scholar, Social Work Abstracts Plus, CINAHL Plus, and ProQuest Dissertations, and Tes databases using the keywords including happiness, joy, humor, immune system, health, and physical health. The search was limited to English and Persian language journals, and there was no time limit. The papers whose content was more relevant to the topics of happiness, humor, health, and immune system were then selected from the papers found and reviewed.