The invention relates to a method of producing hyaluronic acid comprising (1) a step of transforming a plant cell using an expression recombinant vector comprising (i) a DNA encoding hyaluronic acid synthase or (ii) a DNA encoding a polypeptide having an amino acid sequence having one or more amino acid deletions, substitutions, additions or insertions in an amino acid sequence of the hyaluronic acid synthase and having an activity of synthesizing the hyaluronic acid, (2) a step of growing a transformant obtained by transformation, and (3) a step of separating the hyaluronic acid produced by the transformant.