In wireless communications, cooperative diversity schemes has attracted much attention as an SNR improving technique in multi-hop transmission recently. However, in the multi-hop transmission, usually a relay terminal can decode the forwarding information, which can be a problem in terms of security. In current wireless communication systems, the security is ensured at upper layer protocols. These secure protocols are never exclusive and multiple uses of them are rather desirable as a firmer security is provided. Hence, a physical layer security in conjunction with upper layer security is also important. If the physical layer security is provided, an encrypted relaying can be composed, but there are few studies in conventional works. Therefore in this paper, we propose a secure cooperative relay transmission scheme using chaos multiple-input multiple-output (C-MIMO) scheme in which the relay terminal cannot decode the forwarding information but a cooperative diversity effect and a chaos coding gain are obtained at the destination terminal. C-MIMO is a chaos-based encrypted coded-modulation applied to each transmit antenna of MIMO. By utilizing it into a dual-hop amplify-and-forward (AF) relaying, the physical layer security, coding gain, and cooperative diversity are obtained. We show the performances of the proposed scheme by computer simulations.