PURPOSE: To obtain a 2-oxetanone composition having excellent storage stability of 2-oxetanone, effective for separating 2-oxetanone in high purity, suitable for vapor-phase polymerization and useful as a raw material for a biodegradable polymer by adding a specific amount of a specific acid anhydride to 2-oxetanone.

CONSTITUTION: This 2-oxetanone composition is produced by incorporating 2-oxetanone with 0.001-20wt.% (based on 2-oxetanone) of a cyclic carboxylic acid anhydride such as a compound of formula I [R1 to R4 each is H, a 1-18C (un)saturated aliphatic hydrocarbon group such as methyl, ethyl and octyl, an aromatic hydrocarbon group such as phenyl, etc.] and a compound of formula II (R13 to R16 are R1 to R4).