A good characterization of a reservoir is required to understand its properties. One of the methods known is Rock Physics Template (RPT). This method attempts to characterize a reservoir in order to predict the behavior of the reservoir under different porosities and water saturation. However, most of RPT technique applications are limited to granular rocks and not for carbonates. Although carbonates generally suitable as reservoir rocks, it is proven to be more challenging. The complex system of carbonates porosities often gives scatter pattern on the correlation between porosity and P-wave. Therefore, this research attempt to use RPT to model carbonate reservoir. We use Kuster Toksoz as the basis for carbonate rock modeling with the help of the Biot-Gassmann equation. The target of this paper is the Baturaja formation that is located in South Sumatra Basin. This formation is known to be a carbonate reservoir that has produced gas hydrocarbon. This study offers an approach on how to better understand the application of RPT on carbonate formation. Based on the RPT modeling done in this research, specific parameters need to be obtained in order to develop a functional RPT model. These parameters are the aspect ratio of the porosities and the elastic modulus of the minerals.