© 2021 American Society of PeriAnesthesia NursesPurpose: This study aimed to determine the effect of progressive relaxation exercises on physiological parameters, pain, anxiety, and serum cortisol levels in patients undergoing colorectal cancer surgery. Design: This study is a randomized controlled study and has been registered at the Clinical Trial Registry Center (ID: NCT04731428). Methods: The study was conducted on 63 patients (experimental group = 31, control group = 32), who were scheduled for elective laparoscopic-colorectal surgery in the general surgery clinic of a university hospital in Istanbul between March 2018 and May 2019 and met the inclusion criteria. The patients in the experimental group were given progressive relaxation exercises for 15 minutes preoperatively and on postoperative days 1, 2, and 3 after breathing exercise training. The routine treatments and care process of the patients in the control group were maintained. The preoperative and postoperative pain and anxiety levels of both groups were evaluated. Blood pressure, heart rate and respiratory rate, oxygen saturation, and serum cortisol levels were measured at certain time intervals before and after the relaxation exercise. Findings: The patients in the experimental group had lower postoperative pain and anxiety levels and a lower rate of using opioid analgesic on postoperative day 0 compared to the control group. Progressive relaxation exercise had no statistically significant effect on serum cortisol or physiological parameters (P >.05). Conclusions: Progressive relaxation exercise did not affect cortisol levels and vital signs but decreased pain and anxiety, and relatively increased tissue oxygenation, appearing an effective, safe, and practicable nursing intervention.