This cellulose acetate has a total degree of acetyl substitution of 1.75 or more and 2.55 or less, and a degree of acetyl substitution at 2-position or a degree of acetyl substitution at 3-position is 0.7 or less. This cellulose acetate composition includes the cellulose acetate and an additive. The additive is one or more selected from the group consisting of (a) substances of which a pH of a 1 wt. % aqueous solution at 20° C. is 8 or more, (b) substances that dissolve in water at 20° C. in an amount of 2 wt. % or more, and (c) substances that exhibit biodegradability in seawater.