Abstract: Water absorptior of the caboidal spccimens of chopped-glassfiber reinforced polysulfone (FR-PSu) and polycarbonate (FR-PC) in distilled water has been studied.Water absorptipon equation of the materials is similar to heat conduction equation.It is cepressed by a equation which is consisted of three water absorption equarions of one dimension specimen.At initeal stagd of water absorption it is coincident with Chi-hung Shen's equation.Therefore,the diffusivity and equilibrium water content can be deduced from the data.