The compositions of approximately 70 naturally quenched melt inclusions in olivine, clinopyroxene, orthopyroxene, and plagioclase phenocrysts from tephra of the soil–pyroclastic cover of Simushir Island (Central Kuril Islands) were studied. The concentrations of the major rock-forming components, H2O, S, and Cl were analyzed in inclusions. The reconstructed melts contain 48.6–78.4 wt % SiO2, 0.3–8.26 wt % MgO, and 0.12–1.72 wt % K2O. The concentration of S and Cl in the melts changes regularly with increasing SiO2 content: from 0.14 to ~0.02 wt % S and from ~0.05 to ~0.28 wt % Cl. The content of H2O in parental melts is 4.2–4.5 wt %.