Early diagenetic pyrite forms as a result of microbial processes in sediments, but has received little attention as a potential source of microbial fossils. Sedimentary pyrite grains, Archean to Jurassic in age, were examined by scanning and transmission electron microscopy (TEM). Ion milling was essential for the preparation of electron transparent TEM samples. Most pyrite grains revealed coccoid, rod-shaped, and even filamentous features that are interpreted as microbial. Identification of microbial remains in sedimentary pyrite may greatly expand our knowledge of microbial life in the sedimentary record. Combined with geochemical characterization, the study of pyritized microbes in the geologic record may in the future enable us to interpret changes in geochemical signatures more realistically in terms of different sulfate-reducing communities. Sedimentary pyrite grains may also represent a good prospect to further our knowledge of past life on Mars.