Аннотация:We report on the static and dynamic magnetic properties of quasi-two dimensional honeycomb-lattice silver dellafossite Ag3Co2SbO6. The magnetic susceptibility and specific heat data are consistent with the onset of antiferromagnetic long range order at low temperatures with Néel temperature TN ~ 25 K. In addition the magnetization curves revealed a field-induced (possibly spin-flop type) transition below TN in moderate magnetic fields, suggesting that the magnetic ground state is complicated. The LDA+U calculations corroborate this finding and show that the intralayer exchange J is antiferromagnetic and exceeds 4.5 K. This exchange coupling is likely to be related with superexchange between half-filled t2g and eg orbitals. Electron spin resonance (ESR) spectra have revealed a Gaussian shape line attributed to Co2+ ion in octahedral coordination with average effective g-factor g=2.30.1 at room temperature and shown strong divergence of ESR parameters below ~ 120 K, which imply an extended region of short-range order correlations in the compound studied. Based on the results of magnetic and thermodynamic studies in applied fields up to 9 T we propose the magnetic phase diagram in agreement with our experimental findings.