Introduction . Patients who are under mechanical ventilation in intensive care units need to have nutritional support. Also, feeding methods affect serum phosphorus and glucose levels, which are very important in weaning patients off the ventilator. Thus, this study is to compare the effects of both bolus and continuous enteral feeding methods on serum phosphorus and glucose levels in patients with mechanical ventilation. Methods . In this clinical trial study, 34 patients in the intensive care unit of Imam Khomeini Hospital affiliated to the Tehran University of Medical Sciences satisfied inclusion criteria and were randomly divided into control and intervention groups. Sampling was done between October and February 2018. The intervention group received continuous enteral feeding for one week, and the control group received nutrition by the bolus method. The blood glucose level was measured every six hours, and the serum phosphorus level was recorded at the beginning and the end of the intervention, based on the data entry form with respect to all ethical considerations. Data analysis was done by SPSS-20 software. Results . The serum phosphorus level was significantly increased in the intervention group ( P = 0.004 ) and in the control group ( P 0.001 ) and was compared with the previous intervention. No significant difference was found between the intervention and control groups before and after the intervention ( P = 0.22 ) and also one week after the intervention ( P = 0.14 ). There was also no significant difference between the glucose levels from day 1 to day 7 in the control group ( P = 0.33 ) and the intervention group ( P = 0.086 ). Discussion . Nutritional support in both bolus and continuous methods increased the serum phosphorus level. It indicates the importance of the nutritional method in controlling the phosphorus level in critically ill patients. However, there was no difference between the effects of dietary methods on blood glucose control.