Abstarct: In this thesis a novel picture steganography method using multimodal chaotic maps for improvement of chaotic secure communication is presented. Stego image is sent by modulating parameters of the transmitter. The presented method includes a receiver system for asymptotic convergence as well as estimating uncertain parameters of rossler system. The gain of the receiver system changes continuously by a high order sliding mode adaptive controller (HOSMAC), so that system output errors converges to zero. Convergence analysis is accomplished using Barbalat's lemma. The converged parameters are used to determine the map set that is considered. After deciding map set, Gray level modification for hiding the message is selected and the stego image is produced. Using the synchronization and chaotic modulation method, the proposed method is studied in the field of secure communications.