Objective To investigate the effect and safety of administering magnesium sulphate as a technique of controlled hypotension during functional endoscopic sinus surgery. Methods Seventy-five patients arranged for selective functional endoscopic sinus surgery under general anesthesia, were randomly assigned into three groups: control group, magnesium sulphate group and nitroglycerin group(n=25). The patients of magnesium sulphate group received 10% magnesium sulphate 40 mg/kg before the induction of anaesthesia, and then 15 mg·kg~(-1)·h~(-1) by continuous infusion during the operation. The same volume of 5% glucose was administered to the patients in control group. Constant infusion of nitroglycerin beginning with 1 μg·kg~(-1)·min~(-1) was administered to the patients in nitroglycerin group. The hemodynamic indexes, amount of bleeding, fluid intake, operation time, recovery time, quality of surgery field, muscle relaxation and adverse reaction were recorded. Concentration of Mg~(2+) in magnesium sulphate group were compared before and after surgery.Results The patients in the magnesium sulphate group maintained balanced heart rates during the operation, while the heart rates of patients in control group and nitroglycerin group increased significantly (P<0.01). The patients of magnesium sulphate group had lower amount of bleeding and shorter operation time compared with control group (P<0.01). The quality of surgery field in magnesium sulphate group was significantly better than that in control group (P<0.01). Time for 75% recovery of myokymia and recovery index in magnesium sulphate group was higher than those in control group and nitroglycerin group(P<0.01). No adverse reaction was observed in all groups. Conclusion Magnesium sulphate can be effective and safe for controlled hypotension during functional endoscopic sinus surgery.