Abstract-Public-Key Infrastructure (PKI) is the cornerstone technology that facilitates secure information exchange over the Internet. However, PKI is exposed to risks due to potential failures of Certificate Authorities (CAs) that may be used to issue unauthorized certificates for end-users. Many recent breaches show that if a CA is compromised, the security of the corresponding end-users will be in risk. As an emerging solution, Blockchain technology potentially resolves the problems of traditional PKI systems -in particular, elimination of single point-of-failure and rapid reaction to CAs shortcomings. Blockchain has the ability to store and manage digital certificates within a public and immutable ledger, resulting in a fully traceable history log. In this paper we designed and developed a blockchain-based PKI management framework for issuing, validating and revoking X.509 certificates. Evaluation and experimental results confirm that the proposed framework provides more reliable and robust PKI systems with modest maintenance costs.