Background: When a patient receives mechanical ventilation (MV) support through an artificial airway, the physiological functions of upper airway for conditioning the inspired air will have impaired. To avoid the consequences associated with lack of humidification in mechanically ventilated patients, a variety of humidifiers are used. Nurses should be aware, which is the most suitable type for her patients. Objective: Assess the effect of heated humidifier (HH) and heat moisture exchanger (HMEs) on tracheobronchial secretion viscosity and body temperature among mechanically ventilated patients. Settings: This study was carried out in general ICUs at the Damanhur Medical National institute. Subjects: A convenience sample of 60 adult mechanically ventilated patients from starting day of invasive MV were included in the current study. Tools: One tool was used for data collection. It consists of five parts. Results: Findings of the present study show that the HH group had a higher frequency (63.3%) of thin tracheal secretion viscosity in comparison to the HME (53. 3%). As regard patients' temperature, there was no significant difference between the two groups at the two times of measurements (P=0.817, 0.110). Conclusion: The HH has more positive effect on patients' tracheal secretion than the HME. Recommendations: Conduct protocols to improve the practice regarding HH use for patients with invasive MV.