The formation of silver-ethylene complexes in dehydrated Ag-SAPO-11 molecular sieve have been observed by electron paramagnetic resonance spectroscopy (EPR) after gamma-irradiation at 77 K. Such reactive intermediate can play an important role in catalytic conversion of ethylene on silver loaded molecular sieves. The Ag(C2H4)(2) stabilized inside relatively small channels of SAPO-11 molecular sieve it is observed even at 290 K. The 'gas-phase' geometries of Ag(C2H4) and Ag(C2H4)(2) complexes, and respective hyperfine coupling constants were calculated applying DFT quantum chemical methods. The hyperfine coupling constants calculated for Ag(C2H4)(2) complex of D-2h symmetry are in very good agreement with those obtained experimentally.