In this paper, we tried to develop a high damping material with chlorinated butyl rubber (CIIR) and petroleum resins. It was found that the addition of petroleum resins in CIIR could largely increase the loss factor and broaden the damping range. So a sandwich beam laminated with the new developed material was prepared, and the damping behavior of this sandwich beam was measured by dynamic mechanical analysis (DMA). The influence of temperature, frequency, thickness, and component of damping layer on the structural loss factor eta(s), determined by DMA was discussed based on a theoretical model. (c) 2007 Wiley Periodicals.