First finds of microfossils from the silicified microphytolitic carbonates of the Uluntui Formation in the southwestern Baikal region are described. They are represented by remains of the cyanobacterial com munity that formed microphytolites. These microfossils are accompanied by acritarchs probably belonging to green algae. The silicified microfossils are sufficiently well preserved despite complete and repeated recrys tallization of host primary carbonate rocks. Main phases of secondary mineralization are related to hydro thermal metasomatic processes, which were likely provoked by collisional events on the southern flank of the Siberian Craton in the Silurian.