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The aim of this study is to have a better understanding of the distribution and development of carbonate facies of the Oligo-Miocene Tendehantu and Tabalar (undivided) Formations using field data, petrography, and fossil analysis. Both formations are well exposed in the Landas Area along the eastern tip of the Mangkalihat Peninsula. Sedimentary structures found in the outcrops include parallel-bedding, cross-bedding, and graded bedding. Calcrete and dense vegetation covers some of the outcrops in the area. Based on field observations and petrography analysis, four carbonate facies associations have been identified. The first facies association is the Restricted Circulation and Winnowed Edge Platform facies, interpreted as a carbonate lagoonal to bar depositional environment during early Oligocene. The lower part of this facies group interfingers with silicilastic tidal sediments of the Kuaro Formation. The second facies association is the Open Circulation Shelf facies, interepreted as a carbonate shelf depositional environment with favorable seawater circulation and local patch reef development from Oligocene to early Miocene. During the early middle Miocene, the Foreslope- Toe of Slope Facies Association was deposited. This facies association consists of turbiditic deposits. The last facies association is the Deeper Shelf facies, as indicated by biostratigraphic analysis and the presence of a thick marl deposit conformably overlying the turbidite facies. The two last facies were formed in early Miocene-Pliocene. From facies 1 to facies 4 there is a change from a shallow environment to a deeper environment suggesting a backstepping process on the carbonate platform from early Oligocene to Pliocene in the eastern tip of Mangkalihat. During the course of this study, there is no evidence of a regional Mid Tertiary unconformity in East * Institute of Technology Bandung Borneo nor was a shallowing upward sequence found. Instead, a backstepping carbonate platform, or deepening up-section facies pattern was observed in the Tertiary carbonate sequence suggesting that relative sea level rise was the dominant depositional condition rather than uplift on the carbonate development in the eastern tip of the Mangkalihat Peninsula.