The purpose of this study was to examine the effect of ankle joint angle on the intermuscle difference in postactivation potentiation (PAP) between the medial gastrocnemius (MG) and soleus (SOL) muscles. At the neutral position of joint angle, dorsiflexion of 20 degrees , and plantarflexion of 20 degrees , twitch responses were evoked by stimulating the posterior tibial nerve with supramaximal intensity before and after a 10-s maximal voluntary plantarflexion at each joint angle. Mechanical properties of the MG and SOL muscles were assessed simultaneously and separately by using mechanomyography (MMG), and the extent of potentiation of each muscle was evaluated by peak-to-peak amplitude of the MMG signal. The MG showed greater potentiation than the soleus after the conditioning MVC in the neutral and dorsiflexion position, while in the plantarflexion position no significant difference was found in PAP between MG and SOL. These results suggest that the difference in the magnitude of PAP between synergistic muscles is determined by a combination of the joint angle- and fiber composition-dependence of PAP.