In distributed networks, the signer wants his signature to be verified by anyone in the same group with him and the recipient wants to verify the signature independently. Motivated by this consideration, a certificateless group inside signature is presented in this paper. The signature scheme has the following properties: despite being without certificate, it can provide an assurance to the user about the relationship between a public key and the identity of the holder of the corresponding private key; a signature can be verified independently by any member in the same group with the signer; nobody outside the group can verify a signature. It is only the signer who knows his private key, even the PKG (private key generator) doesn't; any one in or outside the group can't forge a signature of others.