This research was designed to study the change and compare the blood glucose (BS) levels in neuro surgical patients under general anesthesia using sevoflurane or isoflurane. Forty patients were divided by complete random sampling into 2 groups. Both groups received non-glucose intravenous fluid during the pre and intra-operative period. Group I received not more than 2.5% sevoflurane. Group II received not more than 1.5% isoflurane. The inhalation agents were combined with 50-66% nitrous oxide in oxygen. Blood glucose concentration was measured by glucometer before and after induction of anesthesia, then every hour consecutively during anesthesia until the end of surgery. The Student t-test and Chi-square test were used for the statistical analysis.The results showed that hypoglycemia (BS<70 mg%) was found in 5 patients in both groups after induction and 1 st hour of anesthesia. In group I, the blood glucose levels after induction and at 1st hour were significantly lower than that before induction, however, the blood glucose levels at 2nd, 3rd and 4th hour were significantly higher than that after induction. In group II, the blood glucose level at 3rd hour was significantly higher than before induction, after induction and at 1 st hour. There was no significant difference in the mean blood glucose levels between both groups at the same period of time. In conclusion, sevoflurane and isoflurane showed no difference in increasing the blood glucose levels at 2nd and 3rd hour in patients undergoing neurosurgery.