The aim of this research was to develope the additive for physical strength improvement of water soluble fiber(CMC) using viscose rayon. Experimental parameters were reaction time and concentration of MgSO₄. Firstly, solubility of carboxymethylcellulose(CMC) according to the addition of MgSO₄ was tested at room temperature with water. Secondly, through the examination of the FT-IR spectra, absorption band caused by hydroxyl group and carboxyl group was confirmed.