Abstract: Modern travertine deposits are observed in the Sıcakçermik hot springs area located northwest of Sivas, Central Anatolia.They are the carbonate deposits of crustal (spongy) and/or alabaster-textured formations controlled by both organic (the fissure and joint ridges) and inorganic (waterfall or cascade deposits; terrace-mound travertines; and shallow lake fans)processes. They are recognized in the field by special identifying trails such as manganous-ferrous travertine shrubs resembling ivy, siliceous stromatolites, and ferrous pisoids, 3 to 12 mm in diameter.All the recent travertine samples examined dominantly consist of subidiomorphic prismatic-tabular calcite crystals.Scanning Electron Microscopy (SEM) revealed that calcite crystals forming the pisoids are characterized by zonal growth.Stromatolitic formations, on the other hand, bear regular joints developed as a consequence of sudden cooling and some special structures indicative of bacterial activity (in the form of nodule, spheroid, ellipsoid, column, filament and honeycomb orgrape bunch structures). In addition, secondary dissolution vugs and pores giving way to the release of CO2 are associatedstructures with the stromatolitic formations. From stable isotope analyses of the different type travertines 8 I3C values between6.95 and 8.09 %o, and bl80 values between -15.73 and -16.76 %o were obtained.The data collected through all the utilized techniques suggest that the microbiological activities are dominanatly effectivein the formation travertines. It was concluded that travertines were produced by microorganisms referred to as in literaturesulfate-reducing, boring-budding bacteria such as Coccoids, Pedomicrobium, Beggiatoa sp., Thiobacillus sp as well as bluegreen algae (Cyanobacteria). On the other hand, the stable isotope data indicate that water of the hot y ^ is of meteoricorigin and carbonate sediments are accumulated in few 10 years.