The effect of solvent, DMF, and hydrophilic polymer on the hydration melting behavior of Tae Kwang polyacrylonitrile-based copolymer (T-PAN) was investigated by DSC measurement. The melting temperature (T(m)) of T-PAN was sharply lowered by incorporating water under autogenous pressure, but leveled off above a critical water content : 23 wt%. However, an additional incorporation of DMF into the hydrated T-PAN further lowered the T(m), even above the critical water content. On the other hand, addition of water-soluble poly(acrylic acid), poly(vinyl alcohol), and poly(ethylene glycol) or water-swellable starch to the hydrated PAN slightly raised the T(m).