Objective: Frailty has been noticed as an important preoperative risk factor for cardiac surgery. The purpose of this study was to evaluate the effect of frailty on the rehabilitation process and walking ability after cardiac surgery. Methods: A total of 213 patients aged 65 years or older who underwent elective cardiac surgery at our hospital between August 2018 and October 2020 and who underwent a preoperative frailty assessment were included. The patients were divided into two groups: group F with frailty and group N without frailty, and the perioperative factors, postoperative course, and walking ability in both groups were examined. Results: Of all patients, 70 (33%) were diagnosed as frail. In the preoperative factors, gait speed and grip strength were significantly lower in group F, and there were more cases of sarcopenia and malnutrition. There was no significant difference in surgical factors between the two groups, except for a bias in the surgical category. In the postoperative course, there were no significant differences in intubation time, ICU stay, postoperative complications, or hospital stay between the two groups, but more patients in group F were transferred to another hospital. In the F group, the start of walking and the day of achieving 100 m walking were significantly delayed, and the number of patients who achieved 300 m walking was 52 (74%), which was significantly lower than 197 (89%) in the N group. The cutoff value of gait speed was 0.88 m/s. Conclusions: Frailty was associated with delayed rehabilitation and reduced walking ability after cardiac surgery, and increased hospital transfers. In addition, the preoperative gait speed was adopted as one of the factors related to the possibility of a 300 m walk after surgery. We believe that preoperative rehabilitation is a promising strategy to improve the condition of frail patients who require cardiac surgery.