Purpose: The study was conducted to explore experience of using humor among psychiatric-mental health nurses. Methods: Semi-structured in-depth interviews were used to collect data from 30 nurses working in community mental health centers or psychiatric wards. Data were categorized and coded using content analysis. Results: The findings confirm that 11 categories, 43 sub-categories, and 104 statements were drawn from 4 domains. The four domains included effectiveness of humor, effective use of humor, ineffective use of humor, and barriers and promotive strategies to the use of humor. Nurses experienced positive and negative effects of humor. Popular fad words, jokes, imitation, and compliments were identified as effective types of humor. Discounting humor and belittling humor were identified as ineffective types of humor. Effective humor was humor that was used after establishing a trust relationship and when the patient`s mental status was stable. Barriers to using humor were heavy workload, nurses` careful character, and nurses`` concern about patients` responses. Conclusion: Nurses should assess the nurse-patient relationship and patients` mental status when they plan to use humor. In addition, hiring more nurses and providing education about humor are suggested to improve sense of humor and recognize the effectiveness of humor.