Oxygen nonstoichiometry and thermodynamic stability of Zn-doped YBaCo4 (-) xZnxO7 + (delta) oxides were investigated by solid state coulometric titration and EMF-method, respectively. As a result, significant zinc doping was shown to increase the stability of YBaCo4 (-) xZnxO7 + (delta) oxides in oxidizing atmosphere. However enrichment of YBaCo4 (-) xZnxO7 + (delta) oxides by zinc results in increasing their reducibility since the low pO(2) stability limit shifts towards higher pO(2) values upon doping. Substitution of zinc for cobalt in YBaCo4 (-) xZnxO7 + (delta) oxides was also found to narrow their oxygen homogeneity region. Total conductivity and Seebeck coefficient of YBaCo4 (-) xZnxO7 + (delta) oxides were measured simultaneously using 4-probe dc-method. The defect structure of YBaCo4 (-) xZnxO7 + (delta) oxides was successfully analysed using Kroger-Vink approach. The data on oxygen nonstoichiometry, total conductivity and Seebeck coefficient of the thermodynamically stable YBaCo4 (-) xZnxO7 + (delta) (x = 0, 1) oxides were found to be quite consistent with the proposed model of their defect structure.