The present invention provides a cellulose triacetate which exhibits 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 a solid concentration) solution, which is then filtered under a constant pressure at the filtration pressure of 3 kg/cm2 and the temperature of 25° C. using a muslin 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×2×104.