The effect on particle collection efficiency of a ring attached to the upper part of the outlet pipe of a gas cyclone was examined by experiment and CFD simulation. From a visualization experiment using fine bubble foam and CFD simulation, the rotational recirculation region is at maximum near the upper plate and the region decreases to the lower position. For the tapered shape ring of type Dc, the cyclone pressure drop is minimum, because the rotational recirculation region is almost eliminated by use of this special ring. The 50% cut size of the tapered shape ring of type Dc shows a minimum value and maximum particle collection efficiency is obtained. For the tapered shape ring, the optimum wall thickness ratio of the upper part to lower part is 1.47 and maximum particle collection efficiency and minimum pressure drop is simultaneously realized by use of the type Dc ring. The average downward fluid velocity in the upper part of the cyclone for the type Dc ring is greater than that of the case without the ring. Particles tend to go toward the downward direction easily and high particle collection efficiency is achieved for this special ring. The experimental partial separation efficiency qualitatively agreed with the simulation results. (C) 2014 Elsevier B.V. All rights reserved.