Mitsubishi Rayon Company has developed ultra low denier (1 denier per filament) acetate tow to meet a recent strong demand for high removal efficiency filters in low tar cigarettes. To characterize this ultra low denier tow, a quantitative study is made on the performance of filters using several tow items of 5 to 1 filament denier. The filter tips of the 1dpf tow with 10 mm length and 24.2 mm circumference show a pressure-drop of 800 Pa and high removal efficiency of 40% in tar and 70% in phenol respectively. The details of filtration performance and features of the 1dpf tow are introduced as compared with those of several tow items.