Objectives: This study aims to investigate the effects of the "Thank you-Sorry-Love" (TSL®) program on posttraumatic growth (PTG) and cortisol level in parents of children with cancer. Methods: A total of 15 mothers of children with cancer were randomly assigned to the experimental group (n = 7) with the TSL intervention or a control group (n = 8) without any intervention. PTG and cortisol level were checked 3 times at the pretest, posttest, and 10-week follow-up. Results: PTG scores were significantly different between the two groups at the posttest and the follow-up test. Cortisol level was only significantly different between the two groups at the posttest. Conclusions: The TSL program may be a possible intervention for parents of children with cancer.