A PSA air separation process for the production of high purity nitrogen is studied experimentally and theoretically. The experimental apparatus is composed of three columns filled with zeolite X. The PSA cycle consists of six steps : pressurization with air, adsorption, recovery, null, high pressure purge with product nitrogen, and desorption. The nitrogen purity analyzed between 95.0 and 99.992%. The effects of adsorption pressure and reflux ratio on the PSA performance are studied experimentally. The productivity is 2.8 NL/(kg . min) and the recovery is 55% at a nitrogen purity of 99.99% and an adsorption pressure of 800 mmHg. The experimental results are compared with the theoretical model, and the effects of the recovery step and the operating variables on the performance are studied theoretically. The recovery step makes the PSA performance favorable, especially in the high product purity region above 99%.