The wide temperature range at which transitions occur between magnetic structures, and the coexistence of magnetic structures in the UP1−xSxsystem are attributed to the incomplete homogeneity of the powder samples. The inhomogeneity affects the linewidths of the x‐ray diffractometer traces, the31P nuclear magnetic resonance (NMR) lines in the paramagnetic state, and the magnetic properties of UP1−xSx. The firing treatment of UP broadens the x‐ray lines, while a second homogenization of UP0.72S0.28sharpens the x‐ray and31P NMR lines and decreases the portion of the antiferromagnetic structure that coexists with the major ferromagnetic phase at low temperatures. The composition ranges (inhomogeneity widths) deduced from the x‐ray line broadening are about 0.1x0, wherex0is the mean sulfur concentration. The upper limits of the inhomogeneity widths obtained from the excessive31P NMR linewidths and the widths of the magnetic transitions are in fair agreement with the inhomogeneity widths based on the x‐ray data.