The human serum proteome is closely associated with the state of the body.Endogenous peptides derived from proteolytic enzymes cleaving on serum proteins are widely studied due to their potential application in disease-specific marker discovery.However,the reproducibility of peptidome analysis of endogenous peptides is significantly influenced by the proteolytic enzymes within body fluids,thereby limiting the clinical use of the endogenous peptides.We comprehensively investigated the N and C terminus of endogenous peptides using peptidomics.The cleavage site pattes of the N and C terminus and adjacent sites from all the identified endogenous peptides were highly conserved under different sample preparation conditions,including long-term incubation at 37℃ and pretreatment with repeated freeze-thaw cycles.Furthermore,a distinguishable cleavage site patte was obtained when a different disease serum was analyzed.The conserved cleavage site patte derived from proteolytic enzymes holds potential in highly specific disease diagnosis.