The present invention provides a method for analyzing protein using a Biuret reaction, which can prevent coagulation of protein and an increase of a viscosity of a reaction liquid caused thereby, even when using a sample including protein with a high concentration. A sample including protein is adjusted to be alkaline by adding a sodium hydroxide solution or the like, to which a divalent copper salt and a salt containing a chaotropic ion are added so as to cause a Biuret reaction, and a degree of coloring thereof is measured, thereby analyzing the protein. The chaotropic ion may be, for example, a SCN ion, an I ion, a NO3 ion, a ClO4 ion, a Br ion or a Cl ion.