This paper introduces a spectrum sharing system for Micro Operators (MOs) using the blockchain network. In order to satisfy different network requirements for each service, the license for spectrum access should be dynamically allocated to the required spectrum bandwidth. We propose a spectrum lease contract for MOs to share spectrum with the Mobile Network Operator (MNO) is performed through the blockchain networks. Main reasons for applying the blockchain network to the spectrum sharing system are as follow. First, the blockchain networks share database with all participants. Second, networks have mutual trust among all participants. Third, it needs no central authority. Fourth, automated contract execution and transaction interactions are possible. The blockchain usage in the MO-based spectrum sharing system and the detailed process of spectrum lease contract are proposed. Then, the economic effects of spectrum sharing system for MOs is analyzed. The MO can be profitable by getting involved in the blockchain to take reward for a Proof of Work (PoW) and providing wireless service to its users.