For the first time, we present our findings of the origin of sulfur in the gypsum and native sulfur within the Plesenci deposit, R. Macedonia. There we made a series of complex research and analysis of the light isotope (S-32), heavy isotope (S-34), and their isotopic ratios (delta S-34). For the gypsum within the ore deposit Plesenci, delta S-34 values ranged from -7.1 up to -3.2 parts per thousand (standard deviation not higher than +/- 0.9), averaging -5.5 parts per thousand, while those for native sulfur have shown range starting from -1.00 up to +2.8 parts per thousand averaging 0.5 parts per thousand (standard deviation not higher than +/- 0.8), due to enrichment with lighter sulfur isotope and relative enrichment with heavy sulfur isotope, respectively. Those ranges of sulfur isotope ratios indicated that the origin of sulfur could be related to deep sources. (C) 2015 The Authors. Published by Elsevier B.V.