Catalysts with the Mo1V0.3Te0.23Nb0.12Bi0-0.05 compositions were prepared via spray-dry method and tested in ethane oxidative dehydrogenation (ODE) reaction. The catalysts were characterized by XRD, HRTEM, SEM and XPS. A strong effect of the bismuth content on physicochemical and catalytic properties was observed. At low Bi concentrations (Bi/Mo = 0.004-0.075) the M1/M2 ratio, morphology and dispersity of the M1 phase changed resulting in a decrease of the catalytic activity. The maximum activity, selectivity to ethylene and stability in reaction conditions were obtained at intermediate Bi concentrations (Bi/Mo = 0.015-0.025). These samples had the highest M1 amount among modified samples. Hindering of Te segregation along six-membered channels of the M1 phase preventing the Te loss was detected. Bi incorporation in such channels and its possible participation in active ensembles are assumed to be responsible both for the stability and enhanced catalytic properties of the M1 phase. A further increase of the bismuth content (Bi/Mo = 0.05) was accompanied by a decrease of the M1 particle size and structural disordering. Suppression of the M1 phase crystallization and formation of less active and selective M2 and M5O14 phases (M-Mo,V,Nb) were observed at the maximum bismuth content. (C) 2017 Elsevier B.V. All rights reserved.