The present invention provides a cellulose triacetate exhibiting a satisfactory filtration performance. Thus, the present invention provides a cellulose triacetate whose occlusion constant (K) determined by the following method is 70 or less.
Method: the cellulose triacetate is dissolved in a solvent mixture of methylene chloride/methanol (=9/1 w/w) to form a 16 % by weight (as solid concentration) solution, which is then filtered under a constant pressure at the filtration pressure of 3 kg/cm 2 and the temperature of 25°C using a musulin filter to determine a filtered volume with the lapse of time, from which the slope of a linear curve represented by t/V - t (wherein t is a filtration time (sec) and V is a filtered volume (ml)) is calculated to obtain an occlusion constant (K) where K=slope x 2 x10 4 .