New phospho-silicides RhSi3P3 and IrSi3P3 were synthesized and their crystal structures were determined by single crystal X-ray diffraction techniques. Both compounds are isostructural at room temperatures and crystallize with the monoclinic symmetry in the space group C2. Lattice parameters are a = 6.626(1) Angstrom, b = 7.210(1) Angstrom, c = 5.522(1) Angstrom and beta = 118.31(1)degrees for RhSi3P3 and a = 6.577(2) Angstrom, b = 7.229(2) Angstrom, c = 5.484(2) Angstrom and beta = 117.91(2)degrees for IrSi3P3. The crystal structure can be described by separated octahedra of Si or P atoms surrounding metallic atoms Rh or Ir. The octahedra are connected to each other by chains,of type M-Si/P-Si/P-M. The atoms of P and Si are fourfold coordinated.