Provided is a method for quantifying urea in a sample solution with a colorimetric method using diacetylmonoxime, wherein a reagent formulated for use in reaction is refrigerated, and the refrigerated reagent is used to quantify urea. In particular, an antipyrine-containing reagent solution is maintained at, for example, 20oC or lower after being formulated and until the solution is used to quantify the urea.
