Environmental perturbations at mass extinction events are reviewed based on isotopic compositions of sulfur and carbon. Large negative excursions in marine carbonate δ¹³C are commonly associated with mass extinctions. The δ¹³C excursion after the Cretaceous-Teriary (K-T) boundary event has been linked to a collapse of the vertical carbon isotope gradient. As a vertical carbon isotope gradient is a function of photosynthetic productivity, the collapse of the isotope gradient implies cessation of photosynthesis. Some mechanisms for the decrease in sunlight after the K-T impact event were proposed so far, such as dust cloud, sulfate aerosol, and soot from global wildfires; however there is no consensus for the cause of the cessation of photosynthesis. Both two major events that can initiate mass extinctions, i.e., bolide impact and intense volcanic activity, should release sulfur-bearing gases into the atmosphere. Such gases should be converted to sulfate aerosol and, eventually, sulfuric acid rain, which raises sulfate concentration in freshwaters. Increase of sulfate concentration in freshwaters enhances accumulation of sulfide produced by sulfate-reducing bacteria. Actually, sulfide enrichments were observed in the sedimentary rocks from the terrestrial K-T and Permian-Triassic (P-T) boundary sections. The duration of the sulfide enrichments can be used for the discussion of the causes of the mass extinction events.