According to a method for monitoring post-translational modifications of protein is provided, a first microbead by binding a protein antibody to a base bead is provided. A second microbead by binding a target protein having a first post-translational modification or a second post-translational modification, which are inversely proportional to each other, to the protein antibody of the first microbead, is provided. A third microbead by binding the second microbead to a first post-translational modification antibody is provided. A fourth microbead by binding the second microbead to a second post-translational modification antibody is provided. Impedances of the third and fourth microbeads are measured. A ratio of a first difference, between the impedances of the third microbead and a reference impedance, to a second difference, between the impedances of the fourth microbead and the reference impedance, is obtained.