Mimetics of antibody-binding sites represent particularly interesting targets,however they are difficult to identify.In most cases,naturally derived CDR3 peptides show a much lower activity and affinity.In this study,we identified a CDR3 domain antibody with framework 3 (FR3) and FR4 in the flank by screening a lysozyme-immunized phage display VHH library.This antibody has a potent enzyme inhibiting activity and high thermal stability.With sequence alignment and sitedirected mutagenic analysis,we found that the cysteine residue at amino acid position 88 in FR3 might play a key role in maintaining the stability of the CDR3 antibody.The small-sized CDR3 domain antibody might act as a new scaffold for affinity transfer,hence making a useful contribution to the understanding of antigen-antibody interactions.