Miscibility of 17b-estradiol and Eudragit 1 RS in solid dispersions was determined by modulated temperature differential scanning calorimetry (MTDSC). A reduction of the 17b-estradiol melting point in Eudragit 1 RS solid dispersions was observed by MTDSC using heating program I in which the maximum temperature in the first heating run was lower than the 17b-estradiol melting point. The melting point depression of 17b-estradiol in solid dispersions as a function of composition could be explained by the Nishi-Wang equation indicating an interaction between 17b-estradiol and Eudragit 1 RS in the system. A variation of glass transition temperature (T g ) of 17bestradiol in Eudragit 1 RS solid dispersion was observed by MTDSC using heating program II in which the maximum temperature in the first heating run reached the 17bestradiol melting point. In the second heating run of heating program II, 17b-estradiol was in an amorphous form blended with Eudragit 1 RS. The variation in T g of amorphous 17b-estradiol blended with Eudragit 1 RS could be explained by the Kwei equation, a modified version of the Gordon-Taylor equation. The parameter estimates from the Kwei equation were consistent with an interaction between 17b-estradiol and Eudragit 1 RS, which was due to inter-associated hydrogen bonding as deduced from the FTIR spectra of the blends.