Kinetics of isothermal (500, 600, and 650°C) oxidation of YCu$_{1-x}$Ga$_x$ (0 $\leq x \leq$ 0.3) solid solution powders (50 $\mu$m of size) on the base of YCu compound is studied by the periodic weighment method as well as by XRD phase analysis. Features of oxidation mechanism of these intermetallic powders are revealed, including two stages of oxidation process. The initial stage of oxidation is characterized by the decomposition of the YCu$_{1-x}$Ga$_x$ solid solution into Y(Cu, Ga)$_2$ phase and individual metals with gradual formation of a stable oxide scale (containing Y$_2$O$_3$ mainly). The second stage of oxidation is characterized by oxidation of the Y(Cu, Ga)$_2$ phase with formation of both copper and gallium oxides. This polyphase oxide scale forms significantly retards either the diffusion of atmospheric oxygen atoms along the grain boundaries or the oxidation. In a whole, the oxidation rate of the YCu$_{1-x}$Ga$_x$ solid solution decreases with an increase in the gallium content, while the apparent activation energy of oxidation increases. That is, gallium dopants increase the resistance to high-temperature oxidation of the YCu phase under its annealing at 500–650°C in air.