BACKGROUND: Chemotherapy is associated with a wide range of physical and psychological side effects, so complementary and alternative therapies may be practiced as an independent treatment or combined with the standard ones to improve health-related quality of life of cancer patients. Laughter yoga has predominantly been used as a complementary therapy to enhance health and wellbeing of ordinary people and patients with chronic diseases. However, to date, few studies have evaluated the effects of this modern exercise on cancer patients undergoing chemotherapy in clinical settings, to the best of the authors' knowledge. the present study aimed to investigate the effects of Laughter Yoga on the health-related quality of life of cancer patients undergoing chemotherapy. METHODS: This study was a two-group randomized clinical trial on 69 cancer patients undergoing chemotherapy at Reza Radiotherapy and Oncology Center, Iran in 2018. Patients were randomly divided into intervention and control groups. The intervention group received laughter yoga for four sessions at one-week intervals. Each session consists of one part and lasts for 20-30 min. Patients' health-related quality of life was assessed before and after the laughter yoga sessions using Quality of Life Questionnaire European Organization for Research and Treatment of Cancer (EORTC QLQ-C30) version 3.0. SPSS Statistics (v.20 software was used to conduct Chi-square, independent t-test, Mann-Whitney, Wilcoxon and paired t-tests analyses of the data. RESULTS: The number of participants in intervention and control groups were 34 and 35, there was no significant difference of demographic and disease related characteristics and pre-intervention HRQOL between two groups. In the intervention group, there is significant difference between pre- and post-intervention scores (Mean ± Standard Deviation) of emotional functioning (12.99 ± 10.49), physical functioning (0.78 ± 6.08), role functioning (3.43 ± 7.97), fatigue (-8.82 ± 22.01), pain (-8.33 ± 11.78), sleep disturbance (-15.68 ± 18.77), and global health and quality of life (6.37 ± 5.04) (p < 0.05). There was no significant change in the control group. Participants reported no adverse events. CONCLUSIONS: A structured laughter yoga intervention in a hospital setting effectively improved health-related quality of life for cancer patients undergoing chemotherapy. Benefits to many patients could be expected if this would become a part of routine care. TRIAL REGISTRATION: This study was registered in the Iranian Registry of Clinical Trials (no. IRCT20180429039463N1) on 21/08/2018.