Gentle thermolysis of the complex, trans-bis(ethylenesulfido)[(octaethylporphyrinato)ruthenium(II)] (1) unexpectedly yields a sulfur-atom-bridged dimer, (mu-sulfido)bis[(octaethylporphyrinato)ruthenium(III)] (2). Compound 2 represents the first example of a structurally characterized unsupported sulfur atom bridge between two ruthenium centers. The Ru-S-Ru bond angle is 135.7 degrees, in marked contrast to the nearly linear Fe-O-Fe bond in homologous [Fe(OEP)](2)O.