Aiming at construction of robust molecular architectures having an active center surrounded by stable walls, a box-shaped cobalt (II)-rhodium (III) pentaporphyrin [Co(tpyp)][Rh(tpp)Cl](4) (2) (tpyp = 5,10,15,20-tetrapyridylporphyrinato dianion, tpp = 5,10,15,20-tetraphenylporphyrinato dianion) was newly synthesized via coordination bonds. The cobalt(II) center of the complex 2 reacts reversibly with O-2 to give a corresponding dioxygen complex of [Co(tpyp)(py)(O-2)][Rh(tpp)Cl](4) (2(py)(O-2)) at low temperatures in dichloromethane-containing pyridine.