Coprecipitates of chlorpropamide (CPA)-sodium deoxycholate (DC-Na) were prepared at various ratios of CPA to the DC-Na. The X-ray diffraction and DSC measurements indicated that CPA in 1:1 and 1:3 w/w CPA-DC-Na coprecipitates did not exist in amorphous form, but the others were amorphous. The dissolution rate of CPA from the CPA-DC-Na coprecipitates increased in distilled water and KP V 2nd disintegration test fluid (pH 6.8), but decreased extremely in KP V 1st disintegration test fluid (pH 1.2). The dissolution rates of CPA-DC-Na coprecipitates were compared with those of CPA alone and CPA-DC-Na physical mixtures. Especially, it was found that the dissolution rate of CPA markedly increased in the case of 1:5 CPA-DC-Na coprecipitate. The concentration of CPA dissolved from CPA-DC-Na coprecipitate reached a plateau within 5-10 min, and thereafter gradually decreased, indicating that CPA released from the coprecipitate was recrystallized.