Pyrite morphology and sulfur isotope composition may serve as indicators of redox conditions changes during sedimentation process. Redox conditions, in turn, affect the accumulation and transformation of organic matter in the rocks. Pyrite morphology was studied with scanning electron microscopy (SEM). Sulfur isotope composition was measured with two methods: Isotope ratio mass spectrometry (IRMS) and secondary isotope ratio mass spectrometry (SIMS). The studied rock samples of the Bazhenov Formation contain various pyrite types: Small (5-10 μm) and large (10-30 μm ) framboids, fine-crystalline (1-2 μm) aggregates and large euhedral crystals (20-50 μm). Small framboids and fine-crystalline pyrite have isotopically light sulfur, δ34S varies in the range from-55 to-20 ‰ CDT. Large framboids and large idiomorphic crystals contain more isotopically heavy sulfur (up to 25 ‰ CDT). The abundance of small framboids indicates anoxic or euxinic sedimentation conditions that control OM's accumulation and preservation. Large framboids and large pyrite crystals in the sediments indicate the suboxic conditions of sedimentation and possible oxidation of OM during early diagenesis.