Abstract: The present study compared the Age of Acquisition (AoA) of words in discourse production by Mandarin aphasia patients with that of healthy controls based on AoA norms. It was found that multi-syllable words in picture description and story-telling tasks as produced by the aphasia group showed lower mean lexical AoA than the control group, but there were no differences between the two groups for single-syllable words in picture description, story-telling tasks and procedure description tasks. The study demonstrates that the AoA of multi-syllable words can serve as an effective indicator for the quantitative assessment of discourse in aphasia.