Abstract: A process for the regeneration of a catalyst by combustion of the coke deposited thereon during a hydrocarbon conversion reaction in which process more than 50 percent of the coke is burned in at least one regeneration chamber operating with a fluidized bed, wherein the upper portion of the fluidized bed the suspension of catalyst particles in said chamber is slowed down due to a substantial increase in the diameter of the regeneration chamber so that the superficial velocity of the rising fluids which no longer contain any oxygen is reduced to a value ranging from 0.5 to 1.5 meters/second, that is, to a value corresponding to the fluidization conditions in a dense fluidized bed.