Objective：To compare the accuracy of end - tidal carbon dioxide partial pressure（P_ETCO₂）and transcutaneous carbon dioxide partial pressure（P_TCCO₂）in predicting arterial carbon dioxide pressure（P_aCO₂）in patients undergoing retroperitoneoscopic urologic surgery. Methods：Fifty patients undergoing retroperitoneoscopic urologic surgery under general anesthesia were included. Values of P_aCO₂，P_ETCO₂，and P_TCCO₂ were measured before and 30，60，90 min after insufflation. The differences between P_aCO₂-P_ETCO₂ and P_aCO₂-P_TCCO₂ were calculated. Correlation and regression analysis were conducted between P_aCO₂ and P_ETCO₂，as well as between P_aCO₂ and P_TCCO₂. Bland-Altman analysis was used to assess the agreement between P_aCO₂ and the other two variables. Results：The absolute differences of P_aCO₂-P_ETCO₂ and P_aCO₂-P_TCCO₂were（13.20 ± 4.43）mmHg and（4.35 ± 2.56）mmHg，respectively（P ＜ 0.05）. The correlation coefficient between P_aCO₂ and P_ETCO₂was 0.79（r ² =0.62，P ＜ 0.001），and between P_aCO₂ and P_TCCO₂ was 0.91（r ² =0.83， P ＜ 0.001）. The 95% limits of agreement between P_aCO₂ and P_ETCO₂ were 4.53 to 21.88 mmHg and between P_aCO₂ and P_TCCO₂ were -3.18 to 10.48 mmHg. Conclusion：P_TCCO₂ monitoring improves the accuracy of estimating P_aCO₂ in patients undergoing retroperitoneoscopic urologic surgery.