The transition phenomenon from deep bed filtration to cake filtration, which is generally observed in the filtration of non-woven fabric filters, was studied in order to clarify the controlling factors and the conditions in which the two stage filtration can be observed. The filtration performances of the suspensions with broad particle size distribution, the monodisperse system of uniform particles, and the binary mixture system of uniform particles were observed with a polypropylene non-woven fabric filter. The presence of both the bigger particle which will be completely captured by the filter, and the smaller particles which can pass through the filter, is a necessary factor for the development of the two stage filtration. The filter life, which is an index of the period of the deep bed filtration, depended more on the amount of filtered bigger particles than on the amount of filtered smaller particles. The specific cake resistance of the cake filtration stage of the two stage filtration was dominated by the smaller particles.