PURPOSE: To prepare high-purity ribonucleic acid with low coloring degree industrially easily and inexpensively, by reacting a ribonucleic acid-containing solution with protease in the presence of a coloring inhibitor.

CONSTITUTION: In preparing ribonucleic acid by reacting ribonucleic acid-containing solution with protein as an impurity with protease, a coloring inhibitor such as sulfurous acid, its salt, or bisulfite, is previously added to the solution, which is reacted with the protease. After the protein decomposition reaction is over, a decoloring agent such as active carbon, ion exchange resin, etc. is used to remove the colored components.