The objective of this study was to develop a rapid-release diazepam suppository. Four kinds of diazepam suppositories were formulated: (1) a conventional suppository with Witepsol H-15 as a base, (2) a conventional suppository with mixed polyethylene glycols as a base, (3) a hollow-type suppository with Witepsol H-15 as a base that contained diazepam solution in its cavity and (4) a hollow-type suppository with Witepsol H-15 as a base that contained diazepam powder in its cavity. The result of the differential scanning calorimetry thermograms indicated that diazepam dissolved in Witepsol base had a strong affinity to the lipophiic base while diazepam dispersed in polyethylene glycol base was still in the crystalline form. The release study of prepared suppositories showed that the release of diazepam from suppository 1 and suppository 4 was very slow. The diazepam released from suppository 2 after 5 minutes was about 30%. The diazepam released from suppository 3 after 5 minutes was about 85%, which was significantly faster than that of the other three formulations (1, 2, and 4). The hollow-type suppository that contained diazepam solution was found to be the most effective rapid-release formulation.