PURPOSE: To provide the subject composition which improves mechanical properties and biodegradability, has high reproducibility, and is useful for biomedicine use such as bone cement by specifying a ratio of the terminal groups and a weight and number averages of molecular weight.

CONSTITUTION: The objective composition has a preferable weight average molecular weight (Mw) of about 500-3000 and a number average molecular weight (Mn) of about 300-2000, and consists of a polymer of fumaric acid and propylene glycol, having 1-2 mmol, preferably 1.3-1.6 mmol, of carboxylic acid terminal groups per 1 g of the polymer. The composition preferably has mechanical strength of 10-25 MPa and, when producing, preferably contains the reaction product wherein a ratio of fumaric acid to a compound selected from the group consisting of bispropylene glycol fumarate and MPM pentamer is 0.65:1.