The motions of granular materials in a vertical shaker are complicated. According to the levels of the amplitude of the vibration acceleration, the particle motion phenomena may include the following convective types: heaping; fluidization; segregation; surface wave; and arching. This paper studied the arching phenomena of granular materials in a vertical shaker. The arching motions were investigated by high speed photography and image processing technology. The velocity fields of the granular materials during vibration were calculated from the recorded images. The ensemble average velocities in the horizontal and vertical directions were close to 0. The velocity fluctuations were also measured. The ensemble average granular temperature increases with the amplitude of the vibration acceleration, however, the variation of granular temperature with the acceleration in the horizontal direction is not as significant due to the existing side walls. (C) 1998 Elsevier Science S.A. All rights reserved.