Experiments were carried out to study effect of vacuum conditions over hydrodynamics of fluidization in large particle beds. Fluidization is one of the most attractive industrial processes due to its very high rates of heat and mass transfer provided by a good contact between particles and fluid. A series of experiments was carried out to analyze the hydrodynamics of a vacuum fluidized bed. A fluidization column, made of glass, with an i.d. of 100 nun was employed and the vacuum conditions were established through a vacuum pump. The tests were run with 10 different types of large particles (2250-7730 mum) under various temperatures and vacuum pressures. Experimental results show that the minimum fluidization velocity increases, decreasing the operation pressure. This tendency fully confirms the results obtained by Llop et al. [Chem. Eng. Sci. 51 (1996) 5149] under vacuum conditions. Using the experimental results two equations, one for sharp particles the other one for round particles, were developed to predict the minimum fluidization velocity and the results were compared with the other equations proposed in the technical literature, On the other hand, the experimentally obtained values of bed voidage under minimum fluidization conditions were found to be insensitive to operation pressure as also observed by Chitester et al. [Chem. Eng. Sci. 39 (1984) 253].