The invention provides a maleimidyl-containing material having a substituent group defined by the following structural formula (1) containing a maleimidyl group (maleimido group): ##STR00001## wherein A denotes a spacer containing an amino acid or a peptide spacer P.Also, the invention provides a production method of the above-mentioned maleimidyl-containing material involving a step of reacting a material containing an amino acid or a peptide chain with a compound containing a maleimido group.