Aims. This study aimed to analyze the effects of the surgery preparation time on patient outcomes. Background. Postoperative complications have a decisive effect on postoperative survival. The anesthesia time is a crucial determinant of such complications. Competent operating room nurses can shorten the surgery preparation time, which is the time from when anesthesia is first administered to the making of the surgical incision. The shortening of this preparation time can shorten the anesthesia time and may reduce postoperative complications. However, discussion of this preparation time is insufficient. Therefore, this study analyzed the effect of the surgery preparation time on patient outcomes. Methods. From electronic health records data, this retrospective cohort study used the data of 1,944 patients who had been immediately admitted to the ICU after their surgery between 2017 and 2020. The patients were divided into two groups: ≥30 minutes preparation time and <30 minutes preparation time groups. We performed chi-squared tests and t-tests to determine differences in preoperation, intraoperation, and postoperation characteristics of the patients and patient outcomes based on the surgery preparation time. Furthermore, we performed a multiple logistic regression by including 12 adjusted variables to determine the influence of the surgery preparation time on patient outcomes. Results. Among the 1,944 patients, 820 were in the ≥30 minutes preparation time group and 1,124 in the <30 minutes preparation time group. The multiple logistic regression analysis showed that the surgery preparation time affects alertness (OR = 1.44; 95% CI: [1.09, 1.90]), ventilator application (OR = 1.32; 95% CI: [1.03, 1.70]), and length of stay in the ICU (OR = 1.69; 95% CI [1.16, 2.47]). Conclusions. The surgery preparation time affects postoperative patient outcomes. The competence of operating room nurses is the most essential aspect of the surgery preparation time. Implications for Nursing Management. It is important to analyze operating room nurses’ tasks, standardize the tasks, and educate nurses according to their experience level to reduce the surgery preparation time and improve patient outcomes.