The crystal structure of a protonated phthalocyaninatoporphyrinato Tb(III) double-decker complex, [Tb(TPP)(HPc)] (1) (TPP: 5,10,15,20-tetraphenylporphyrin, Pc: phthalocyanine), was determined. Crystal structure analysis demonstrated that the proton exists on the meso-nitrogen of the phthalocyanine ligand, and the coordination mode is a nearly ideal square-antiprismatic one. We have also demonstrated that 1 shows single-molecule-magnet (SMM) property, although protonated homoleptic porphyrin Tb(III) double-decker complexes are SMM-inactive. This difference is attributable to the highly symmetric coordination structure of 1.