The present invention relates to can be at least one nucleophilic group reacts present in peptide or protein matter conjugation reagents, it includes at least one leaving groups, the leaving group loses when reacting with the nucleophilic group, wherein the leaving group includes the-parts (CH2CH2O) n-, and wherein n is 6 or bigger numerical value And the new method of the conjugate comprising peptide or protein matter is prepared using such reagent.