Abstract-We propose a new efficient identity-based key-insulted multisignature scheme for facilitating group-oriented applications and mitigating the impact of key exposure. Integrated with identity-based systems, the proposed scheme adopts explicitly verifiable public keys without additional certificate. Each user can also periodically update his private key while the public one remains unchanged. In the proposed scheme, a valid key-insulted multisignature must be cooperatively generated by all signers. Our scheme has the properties of unbounded time periods and random-access key-updates. We also demonstrate that our scheme has better efficiency as compared with previous works and formally prove its security of unforgeability against existential forgery under adaptive chosen-message attacks (EF-CMA) in the random oracle model. Index Terms-Identity-based, key-insulated, multi-signature, key exposure, bilinear pairing.