PURPOSE: There are no sufficient evidences for the sedative effect of gabapentin during anesthesia, especially intravenous sedation (IVS). The purpose of this study was to evaluate the sedative effect of gabapentin as preanesthetic medication during the IVS with propofol. METHODS: 10 volunteer subjects joined this study. They underwent propofol IVS three times on separate days. On the first day, the IVS without gabapentin was performed as a control. On the second and the third day, gabapentin 200 mg and 400 mg were administered before the IVS, respectively. The target blood concentration (CT) of propofol was gradually increased, and the bispectral index (BIS) value and Ramsay sedation score (RSS) were evaluated at each propofol CT. Postanesthetic complications and influences on vital signs were also evaluated. RESULTS: Compared to the control group, the propofol CTs in the gabapentin 400 mg group significantly reduced at the BIS values of 60 and 70 (p = 0.031 and p = 0.043, respectively), and at RSS 3, 4, 5 and 6 (p = 0.040, p = 0.004, p = 0.001 and p = 0.004, respectively). There was no significant difference in propofol CTs between the control group and the gabapentin 200 mg group. There were no abnormality and no deterioration in circulation and respiration in all groups. There were no significant increases in complications with the administration of gabapentin. CONCLUSION: The oral administration of 400 mg dose of gabapentin reduced the propofol CTs for achieving an adequate sedation level on IVS.