Daidzein-PVP coprecipitates were preparated by solvent evaporation method. X-ray diffraction and microscope studies indicated that the ratio of PVP should be up to 1:5 (daidzein:PVP) to form the coprecipitates. Dissolution test, in vitro, indicated that the percent of dissolved daidzein increased remarkably by coprecipitation. The tablets made of the coprecipitates with some excipients released daidzein rapidly. Near complete release (90%) was obtained in about one hour when tested in water or simulated intestinal liquid.