The present invention relates to a preparation method of an organic zinc catalyst capable of preparing an organic zinc catalyst having a finer and more uniform particle size and more improved activity during a polymerization process for preparing a poly(alkylene carbonate) resin, and a preparation method of a poly(alkylene carbonate) resin using the organic zinc catalyst. The preparation method of an organic zinc catalyst includes reacting a zinc precursor and a dicarboxylic acid in the presence of a dispersant to form a zinc dicarboxylate-based catalyst, wherein a reaction step is performed under a condition at which the number of moles of the dicarboxylic acid present in a reaction system is larger than that of the zinc precursor throughout the entire reaction step.