Abstract：It is observed that there can be a strong spin valve effect in organic materials, showing that organic materials can be promising for spintronics applications. The mechanism and efficiency of spin injection into organic materials, however, is largely unknown. Using spin- and time-resolved two-photon photoemission (STR-2PPE) spectroscopy, we have investigated spin injection from Co and GaAs to organic semiconductor copper phthalocyanine (CuPc). With STR-2PPE, the dynamics of both electron and spin relaxation can be studied with femtosecond time resolution and high surface sensitivity. We observed that the spin injection efficiency for hot electrons in is high, ~90% from Co to CuPc. We also observed that the spin polarization increases with time at low energies, revealing scattering processes that can be strongly energy-dissipating but spin-preserving.