—The IEEE 802.16 standard (commonly known as WiMAX), which has been proposed as a new wireless broadband standard, is capable of delivering very high data rate and covering wide area. Video multicast service would become one potential application over WiMAX with the popularity of streaming applications in the Internet. Our method mainly uses adaptive modulation to achieve the goal of rate-adaptive multicast, and combines with the concept of layered multicast. According to the size of video layer, SS distribution, and available symbols, our method adaptively changes the modulations of each video layer in each group of picture (GOP) time. We also propose a Genetic Algorithm (GA) to reduce computational complexity when finding optimal modulation. Experimental results show that the proposed method can achieve promising performance.