This paper shows the performance analysis of a sealless cylinder with a conical type piston and one of three types of rod bearings. The piston without seal is composed of cylindrical and conical portions in the axial direction. The 2D Reynolds equation is solved with a finite difference method for the performance analysis. The relationship between self-centering force and leakage flow rate are investigated. The sealless cylinder fabricated with the proposed optimum design values was tested with three different types of rod bearings having four, five and six pockets respectively. Leakage flow rate tests were conducted to evaluate the performance of the proposed sealless cylinder.