The advent of blockchain sheds light on addressing trust issues of peer-to-peer networks by providing a distributed tamper-resistant ledger. Beyond cryptocurrencies, it is believed that blockchain can also be used to protect other properties such as reputation. Most of the existing studies of enhancing reputation systems using blockchains are built on top of the bitcoin-like blockchains, so they are inherently constrained by the low-efficiency and high-consumption of the underlying blockchain. To fill this gap, we present a reputation-based consensus protocol called Proof of Reputation (PoR), which guarantees the reliability and integrity of transaction outcomes in an efficient way. In PoR, we let reputation serves as the incentive for both good behavior and block publication instead of digital coins, therefore no miners are needed. We also implement a prototype and our scalability experiments show that our protocol can scale to over a thousand participants in a peer-to-peer network with throughput of hundreds of transactions per second.