The effect of the particle size and chemical state of chromium in Cr/SiO2 catalysts with different chromium contents (2-10%) prepared under different conditions upon the properties in the conversion reaction of liquefied petroleum gas (LPG) in the absence and presence of water vapor was studied. It was shown that the degree of conversion of LPG decreases in the presence of water vapor and the selectivity for C-2-C-4 olefins increases over the Cr/SiO2 catalysts with a chromium content of 5-7%.