This study compared the five-word lexical bundles (LBs) expressing gratitude in acknowledgments of dissertations written by Chinese and American PhD students of linguistics. Two corpora were built: (1) The Chinese University Dissertation Acknowledgments Collection (CUC) which contained 700 acknowledgments with a total of 300,686 tokens, and (2) the American University Dissertation Acknowledgments Collection (AUC) which contained 700 acknowledgments with a total of 493,045 tokens. We then retrieved five-word LBs, of which LBs expressing gratitude in CUC and AUC were identified, categorized, and compared with respect to frequency, forms and structures. Major findings were: (1) the Chinese students used a substantially greater number of gratitude LBs than the American students; (2) the two groups used considerably different gratitude LBs; and (3) the two groups mainly relied on verb phrase-based LBs to express gratitude, but the Chinese students used a larger proportion of noun phrase- yet a smaller proportion of verb phrase-based items than the American students; and (4) the two groups used dissimilar structures and words to construct gratitude LBs. These findings enrich our knowledge of linguistic patterns in dissertation acknowledgments as a unique genre of academic prose, and provide corpus-based learning materials for students tasked with properly expressing gratitude in their theses or dissertations.