The present invention provides a method for the measurement of apoB-48, which involves measuring the apoB-48 by diluting a sample with a tris-buffer and, as needed, a surfactant and reacting the diluted sample with an anti-apoB-48 monoclonal antibody, and a kit for measuring the apoB-48 by using the above method. The method and the kit can accurately, rapidly and readily measure the apoB-48 particularly in blood. The method for the measurement of the apoB-48 and the kit to be used therefor are applicable to diagnosis of diseases associated with the apoB-48 and assessment of an efficacy of an ingredient of medicine for treating hyperlipidemia and an ingredient of functional food by measuring an increase or decrease of the apoB-48 in blood.