The combustion of gas-generating compositions (GGC) including composite oxidants (KClO₄/NH₄NO₃) and fuels (methylcellulose, MC; wooden powders, WP) under atmosphere was studied. Results show that for samples of KClO₄/NH₄NO₃-MC with various value of oxygen balance, the combustion rate of samples decreases with the decreasing content of KClO₄ in compositions. Variation of combustion rate of samples KClO₄/NH₄NO₃-WP is more complicated. By analyzing the experimental results, the maximum of combustion rate of samples studied appears at oxygen balance of -15%. This may be concerned with the mass law and the special properties of heterogeneous chemical reactions appeared in condensed phase of burned samples.