[Purpose] To investigate the predictive value of maximum inspiratory pressure (MIP) and the rapid shallow breathing index (RSBI) in a ventilator weaning protocol and to evaluate the differences between clinical and surgical patients in the intensive care unit. [Subjects and Methods] Patients aged ≥15 years who underwent orotracheal intubation for mechanical ventilation and who met the criteria of the weaning protocol were included in the study. Receiver operating characteristic (ROC) curves were calculated for the analysis of each index. [Results] Logistic regression analysis was also performed. MIP showed greater sensitivity and specificity [area under the curve (AUC): 0.95 vs. 0.89] and likelihood ratios (LR) (positive(+): 20.85 vs. 9.45; negative(−): 0.07 vs. 0.17) than RSBI in the overall sample (OS) as well as in clinical patients (CP) (AUC: 0.99 vs. 0.90; LR+: 24.66 vs. 7.22; LR-: 0.01 vs. 0.15) and surgical patients (SP) (AUC: 0.99 vs. 0.87; LR+: 9.33 vs. 5.86; LR−: 0.07 vs. 0.14). The logistic regression analysis revealed that both parameters were significantly associated with the weaning success. The MIP showed greater accuracy than the RSBI (OS: 0.93 vs. 0.85; CP: 0.98 vs. 0.87; SP: 0.93 vs. 0.87). [Conclusion] Both parameters are good predictors of successful ventilator weaning.