Based on COSPEC measurements, the pre-eruptive sulfur content of the magma of the 1991--1995 Unzen eruptions was estimated to be 150 ¿ 80 ppm <Hirabayashi et al., 1995>. However, melt-inclusion analyses of quartz and plagioclase yielded S contents less than 50 ppm, inconsistent with the COSPEC estimate. We extended the melt inclusion analyses to pyroxene phenocrysts, and found that the most mafic melt inclusions in the core zone of a large pyroxene in 1993 dacite have S contents as high as 730 ¿ 100 ppm. By correcting for effect of pyroxene crystallization on the inclusion walls, the least-evolved melt composition was calculated to have S = 390 ppm and SiO2 = 60.5 wt.%, which agrees with the previous estimation about magma-mixing.