The Electron-Spin-Resonance of Mn2+-ions in synthetic cubic and hexagonal ZnS crystals has been observed at X-band frequencies. At 300°K the following values for the parameters of the Spin-HAMILTONian resulted for cubic ZnS: g=2,0024±0,0003, α= +0,000787 ± 0,000006 cm-1, A= -0,00640±0,00001 cm-1. A weak superhyperfine structure due to an interaction of the 3d-electrons of the Mn2+-ion with the surrounding Zn67-nuclei was also resolved. The influence of stacking faults in cubic ZnS crystals on the position and linewidth of the Mn2+-spectrum was investigated in detail. For hexagonal ZnS we found at 300°K: g∥ =2,0018 ± 0,0003, a— F = + 0,000768 ± 0,00001 cm-1, α = +0,000735 ± 0,00001 cm-1, A = —0,00649 ± 0,00001 cm-1, D= —0,01309 ± 0,00003 cm-1, P=+ 0,000010±0,000002 cm-1. The quadrupole coupling constant P was determined from forbidden Am= ± 1 transitions. A strong decrease of the spin-lattice relaxation time of the Mn2+-ion was observed in photoconducting ZnS crystals under uv-illumination at 77°K.