The present invention relates to a water soluble chitosan nanoparticle (WSC-NP) for delivering an anticancer agent and a preparing method thereof, more precisely, a water soluble chitosan nanoparticle for delivering an anticancer agent which has function of targeting on a wanted area by introducing a functional group in the location of highly reactive amine group and becomes an excellent gene carrier with the use of water soluble chitosan since the water soluble chitosan itself can combined with DNA having a negative electric charge(−) owing to the very strong positive electric charge(+) of its amine group, and a preparing method thereof. Therefore, a water-soluble chitosan nanoparticle for delivering an anticancer agent of the present invention can effectively envelope paclitaxel by introducing hydrophilic and hydrophobic groups in the position of highly reactive amine group of the water-soluble chitosan. A water soluble chitosan nanopaclitaxel prepared as the above has an excellent re-dispersion force, after freeze-drying, in distilled water and has an outstanding anticancer effect with its accumulation in tumor cells greater than that of the other anticancer agent carriers.