The depositional environment of Gumai formation is still challenging to be studied. Previous studies of the depositional environment in the Gumai Formation show a debate interpretation of transition, shallow marine, and deep marine environment. The study's objectives are to identify lithology characteristics of Gumai Formation in Baturaja region and determine the potential environment of the Gumai Formation. Miocene clastic sedimentary rocks of Gumai Formation show well-preserved features in Simpang and Muara Dua, South Sumatra. The Gumai Formation discovered in the southern anticline flange, particularly in Muara Dua, composes marl with quartz veins. The opposite flange in the northern part of Simpang region indicates Gumai Formation consists of siltstone, calcareous sandstone, quartz sandstone and sand ball in siltstone layers. Based on the obtained data at Muara Dua and Simpang, the Tertiary rocks of the Gumai Formation are situated in the flange of folded Pre-Tertiary rocks at Garba complex. Gumai Formation in the research area was deposited in transition environment to shallow sea in which the formation in Simpang has shallower marine environment than Muara Dua region.