Background and Objective: Weaning from mechanical ventilator due to the direct effect on patient’s physiologic indices is very risky action and if it is unsuccessful, it can lead to reintubation of patient. The aim of the current study was to compare the effect of two weaning methods from mechanical ventilation “SBT” method with “SIMV” on physiological indices of ventilated patients.Materials and Method: In this clinical trial study, 44 intubated patients in intensive care units of one of the hospital in Arak in 2014 were selected through convenience sampling and then were randomly allocated into two intervention and control groups (each group 22 persons). In intervention group SBT method and in control group SIMV were used as weaning method from ventilation. Data collection was done thorugh using physiological indices and GCS score before, during and after the intervention Data were analyzed by using SPSS 20, paired T-test, independent T-test, repeated measures ANOVA and Greenhouse-Geisser.Results: In SBT group, the means of systolic blood pressure was (107.90±5.2), heart rate (70.27±7.2), respiration rate (14.90±1.06) had significant reduction after intervention (from 9 to 12 Am) (p<0.001). Also, the mean of Pao2 (89.12±1.16), mean of diastolic blood pressure (76.09±4.6), O2 sat (93.09±0.97) and level of consciousness (14.90±0.21) had significant increase after intervention and physiologic status of patients was improved. In control group there was no significant difference among the measured indices.Conclusion: The results showed that “SBT” method leads to improvement of systolic and diastolic blood pressure, heart rate, Pao2, O2sat and level of consciousness of patients in intervention group. It is recommended to apply of this weaning method in intensive care unit.