Degradation of poly(methyl glyoxylate) (PMG) was investigated in vitro in aqueous medium. Various techniques were used to control hydrolytic degradation effects, including weighing (weight loss and water uptake), differential scanning calorimetry (d.s.c.), potentiometry and H-1 nuclear magnetic resonance (n.m.r.). The final degradation products was identified by H-1 n.m.r., using various models such as methylgryoxylate, glyoxylic acid and 2,2-dimethoxy-methyracetate in pure water or acidic medium. Although glyoxilic acid was the final metabolite resulting from degradation, in closed aqueous medium, Various equilibria occurred between degradation compounds. Concerning the degradation mechanism, ester groups are first hydrolysed leading to carboxylic functions followed by chain scissions, by cleavage of acetal bonds, and fast depolymerization.