Role-Based Access Control is an attractive and secure method to access data from cloud storage. Access control method enhances security on Cloud. Role-Based Access Control is a way of authorization in a cloud environment that uses roles as an entity to control the access. Different roles can be assigned to different users based upon their responsibilities in the organization. The present work specifies various policies in Role-Based Access Control on clouds to enhance the existing models. The present work proposed the concept of ontology in which higher authorities can see the data of lower designated officials despite that underneath workers couldn't see the data of higher authorities. The comparison shows that the proposed Role-Based Access control with policy specification and ontology is better than the existing Role-based access control model because the proposed model enhances the security and availability of data on clouds.