When 1-Pheyl-5-Mercaptotetrazole (H (PMT)) was crystallized from solutions, two different types of crystals were obtained, depending on the solvent. One, denoted here by (I), crystallized from e.g . benzene solution, while the other, (II), from aqueous ethanol solution. Comparisons of powder X-ray diffraction patterns, results of elemental analyses, IR spectra and melting (decomposition) points of (I) &(II) showed them to be polymorphs.(I) was triclinic with a =9.403 (1), b =11.867 (2), c =3.9615 (5)Å, α=93.92 (1)°, β=95.66 (1)° and γ =68.32 (1)°, whereas (II) was monoclinic with a =12.2, b = 3.95, c =8.81 Å and β =112°. No refinement of the latter parameters could be made because of difficulties in preparing suitable single crystals. The polymorphs could be converted into each other by recrystallizing from appropriate solvents, but could not by varying the temperature. The melting (decomposition) point of (I) (151°C) was slightly higher than that of (II) (145-146°C), the latter being thermally somewhat less stable.