The vibration-promoted flow of cohesive particulate solids was investigated for limestone and titania powder, each with an average particle size of about I pin. The flow behavior of fine cohesive powders can be improved by the application of harmonic vibrations, as reflected in the flow properties. Based on the work of Roberts (1978, 1984), a shear testing technique has been established that allows the measurement of the effect of vibrations on the flow properties of particulate solids. The experimental results show that the vibration application leads to a significant reduction of the shear strength. The unconfined yield strength decreases with increasing vibration velocity, whereas the angle of internal friction is nearly independent of applied vibration. Also, the unconfined yield strength and the wall friction angle powders can be reduced by applying mechanical vibration. Based on the tab-scale shear tests, the hopper half angle and the unconfined yield strength were estimated. For the given example, the conical outlet width is reduced from 0.88 m to about 0.4 m, and the maximum hopper angle increases from 5degrees up to approximately 20degrees due to the vibration application.