Recently, we have reported the formation of a porphyrin/phthalocyanine heterodimer in which cofacially stacked porphyrin and phthalocyanine are linked together by fourfold rotaxane (Figure 1). Mechanically interlocked supramoelcular linkages such as catenanes and rotaxanes are flexible enough to provide switching properties of the interactions among the components in the assemblies. We have reported supramolecular arrays of porphyrin and phthalocyanine and intramolecular electronic communication between the components. In this paper, we would like to reveal the electrochemical bistability of the porphyrin in the supramolecular assembly of a poprhyrin and a phthalocyanine connected by fourfold rotaxane linkage. Redox bistable systems are capable for taking two stable redox states separated by the energy barrier at the given electrochemical potential depending on the direction of the potential scan. During the negative scan on the cyclic voltammometry of 3, the porphyrin (Por) moiety was reduced into the anion radical (Por•^–) at –1.72 V (vs. Fc/Fc⁺). Por•^– generated was immediately protonated by intra- or inter-molecular proton transfer from the phosporamidate stopper of 3 to afford a neutral radical (PorH•). In the opposite (positive) scan, PorH• was not reoxidized into neutral Por until the potential reached at –0.94 V. Therefore, the two redox states, Por and PorH•, can exist stably at the same potential region depending on the direction of the potential scan.