To obtain a new kind of synthetic polymer showing a bio-absorbable property and capable of being used for the production of a surgical device, etc., by reacting an aliphatic polyoxycarboxylic acid with a diol, etc.

This absorbable polyoxaester contains a first divalent repeating unit expressed by formula I and a second repeating unit selected from a group of formulae II to IV and their combination [R1, R2 are each H, a 1-8C alkyl; R3 is a 2-12C alkylene unit or an oxyalkylene expressed by formula V (C is 2-5; D is 0-2000; E is 2-12 when D=0, and E is approximately 2-5 in other cases); R4 is a 2-8C alkylene unit; A is 1-2000, R5 is CR6R7 (R6, R7 are each H or a 1-8C alkyl), etc.; B is an integer within a range of 1 to (n) for making approximately ≤200000 number average molecular weight of the formula III; P is an integer within a range of 1 to (m) for making approximately ≤1000000 number average molecular weight of the formula IV; G is a residue obtained by removing 1 to L hydrogens from hydroxyl groups of an alcohol having 1-200 hydroxyl groups; L is approximately 1-200 integer].