Background: Bispectral index (BIS) assesses depth of anesthesia. There are controversial reports about opioids, like remifentanil, effect on BIS. At this study, the effect of different doses of remifentanil, 0.1mg/kg/min (LD) and 0.2mg/kg/min (HD) on BIS were evaluated.Materials and Method: 54 patients, ASA Class 1 or 2, age 20-60 years old who were admitted for cataract surgery under general anesthesia were selected. Induction of anesthesia: sodium thiopental 5mg/kg, succinylcholin 2 mg/kg, lidocaine 1 mg/kg and fentanil 2mg/ kg. After tracheal intubations, cisatracuriom 0.15 mg/ kg, propofol 200mg/kg/min and remifentanil HD or LD, each for 10 minutes, with randomized sequences. 4 patients were excluded because they got hypertension or tachycardia more than %20 of baseline or physical movement under general anesthesia.BIS was recorded every one minute. Comparison of mean BIS values of the two groups was made by intra group t-test.Results: Mean BIS in LD group was 51.73±5.87 and in HD group was 45.22±5.2. P-value was <0.001, so the difference was significant.Conclusion: Remifentanil combined with propofol can change BIS, so we can use BIS as an monitoring of depth of anesthesia during general anesthesia with opioids base.