A new analytical procedure based on selective acid hydrolysis was developed to measure the chain length distribution of hard segments(HSCLD) of polyester-polyurethanes. It was tested with polymers made from 4,4’-methylenebis(phenyl isocyanate), 1,6-hexanediol, and alpha,omega-dihydroxypoly-(hexamethylene adipate) with number-average molecular weight 2200. Heating samples with 0.25 M HCl solution in dimethyl sulfoxide with 8.2% water for 36 h leads to nearly complete hydrolysis of the ester groups, leaving the urethanes largely unaffected. The resulting mixture of oligomers can be analyzed by size exclusion chromatography, using dimethylformamide at room temperature as the solvent. Experimentally measured HSCLDs were most often very different from those theoretically predicted for homogeneous reaction.