<p>Medical data sharing in the cloud is crucial for integrated healthcare delivery and improved patient satisfaction. However, transition to cloud-based systems brings critical challenges related to data security and privacy. Protecting sensitive medical information from unauthorized access while ensuring accessibility to authorized individuals demands robust encryption mechanisms. For this purpose, several attribute-based encryption schemes have been suggested in recent years. Nevertheless, careful evaluation of existing schemes demonstrates that they cannot totally provide desired efficiency and security considerations. Therefore, to address the limitation of prior studies,q this paper proposes a highly-efficient and secure scheme for medical data sharing in the cloud by means of the cutting-edge blockchain technology. The proposed scheme offers the following distinct features. First and the foremost, it presents an innovative fine-grained attribute-based encryption method for encrypting medical data before uploading to the cloud. Second, using the concept of partial private keys, we made the scheme escrow-less meaning that trusted key generation centers have no access to private keys of users. Third, by storing public keys in the distributed ledger of blockchain, the proposed scheme simplifies attributes revocation. Finally, the scheme is designed so that can resist well-known attacks, such as collusion and distributed denial of service attacks. Our performed comparative study, including security and efficiency analyses, indicates the suitability and superior stage of the proposed scheme. </p>