The tendering effects of spent laying duck breast muscle by papain and Flavourzyme were researched, changes of myofibril fragmentation index (MFI) and shear force value at proteolysis by two proteiases were compared, and dependence between MFI and shear force value were analyzed. The results indicated that proteolytic degree of spent laying duck breast muscle by papain was more stronger than Flavourzyme, the papain concentrations required to reach same tenderizing effect (i.e. to reach same MFI or shear force value) was about the half of Flavourzyme. There were significant dependence between MFI and shear force value after the duck tenderization. For papain and Flavourzyme, the dependence were -0.965 and -0.950, respectively.