The present invention provides a simple method for the stabilization of a peptide in a biological sample and a reagent for the stabilization, a simple method for the preservation of a biological sample comprising a peptide and a reagent for the preservation, and a method for the accurate measurement of a peptide in a biological sample and a reagent for the measurement. Addition of a saccharide to a biological sample enables the stabilization of a peptide in the biological sample, the preservation of the biological sample comprising a peptide in a stable condition and the accurate measurement of a peptide in the biological sample. As the present invention can stabilize a peptide in a biological sample collected in the clinical examination, the peptide as a marker in the biological sample can be measured accurately in the clinical examination.