Abstract: Peptides, amino acid condensation products, have been widely used in various fields such as disease diagnosis, prevention and treatment, nutrition, cosmetics, and personal care. The rapid development of peptide-associated industries has put forward metrological traceability requirements for peptide measurement activities. Peptide purity measurement is an important technical foundation for achieving SI traceability in peptide measurement activities. The primary methods for measuring peptide purity include mass balance, amino acid analysis, quantitative nuclear magnetic resonance (qNMR), and elemental analysis. To achieve accuracy, consistency, and equivalence in peptide purity measurement results, the Protein Analysis Working Group (PAWG) of the Consultative Committee for Amount of Substance (CCQM) has planned a series of international comparisons on purity assessment for peptides. Currently, the International Bureau of Weights and Measures (BIPM), in cooperation with the National Institute of Metrology, China, and the Health Sciences Authority, Singapore, has organized international metrological comparisons on human C-peptide, oxytocin, and glycated hexapeptide, significantly improving the capabilities of participating laboratories from various countries. This review provides detailed principles, uncertainty evaluations, advantages, and disadvantages of peptide purity measurement methods and carefully introduces the international comparisons on peptide purity measurement. The development trends of peptide purity measurement are discussed, aiming to promote scientific and technological research on peptide metrology.