A process for preparing light olefins from corresponding paraffins consists of reacting said paraffins in a reactor, operating at a temperature of between 450 and 800.degree. C., a pressure of between 0.1 and 3 atm absolute and a GHSV of between 100 and 10000 h.sup.-1, with a catalytic system containing gallium, platinum, possibly one or more alkaline or alkaline-earth metals, and a support consisting of alumina in delta or theta phase or in delta+theta or theta+alpha or delta+theta+alpha mixed phase, modified with silica, the gallium, expressed as Ga.sub.2O.sub.3, being in a quantity of between 0.1 and 33.6 wt %, the platinum being in a quantity of between 1 and 99 ppm, the alkaline or alkaline-earth metals, expressed as oxide, being in a quantity of between 0 and 5 wt %, and the silica being in a quantity of between 0.08 and 3 wt %, the rest to 100% being alumina, and regenerating said catalytic system in a regenerator by burning off the coke which has deposited on its surface, without subsequently reducing it.