Abstract The development of modern technology in recent years, makes the data security very big issue. To secure our data from unauthorized person, encryption is used before transmission. Various sensitive information is using encryption such as: e-mail messages, banking transactions, credit information and military operations. The encrypted data can be in form of text, image, voice, and video. In this paper, a proposed Hill algorithm with chaos system is used to encrypt colour RGB (Red, Green and Blue) image. The key of Hill algorithm is a square matrix. The selection of matrix key numbers is very important. Therefore, chaos system is used to generate sequences of numbers for Hill key matrix. These sequences have a property of randomness that make it very difficult for guessing. Finally, the proposed system is simulated using MATLAB, and a test image is encrypted and decrypted using proposed system successfully.