Graphene has become of great interest in recent years for its unique band structure and prospective importance in both microwave and logic devices. Recently, the use of a boron nitride layer between the graphene and the silicon dioxide substrate has shown enhanced mobilities due to displacing the disorder charge, typical on the oxide, further from the graphene material. 1,2 On the other hand, like the oxide, boron nitride has polar optical modes which can interact with the carriers in graphene to lower their mobility. We have used an ensemble Monte Carlo (EMC technique to study the transport in graphene on a boron nitride layer. Scattering by the intrinsic phonons of graphene, 3 as well as by the flexural modes of the rippled layer, and the remote polar mode of boron nitride has been included. The flexural modes are described by the model of Castro et al. 4 While the EMC uses the simple Dirac band structure, coupling constants for the intrinsic phonon modes are taken by fitting to scattering rates determined from firstJprinciples calculations. 5 We find that, at low temperatures, the mobility is dominated primarily by the intrinsic graphene phonons and the flexural modes. This arises as the interfacial polar mode of boron nitride lies at an energy of 200 meV, which is largely too high to interact well with the majority of the carriers in graphene. On the other hand, at room temperature, the mobility begins to be dominated by the remote polar mode of the boron nitride. Nevertheless, the prospects of reaching a high velocity, needed for device performance particularly at microwave frequencies, remains very good.