Abstract: A cytological study of threatened Carpinus putoensis Cheng and Ostrya reheriana Chun was firstly made in this paper. The interphase nuclei and prophase chromosomes of C. putoensis were categorized to be complex chromocenter type and interstitial type, respectively; the metaphase chromosome number of C. putoensis was reported 2n=14x=112, ranging from (0.920 μm) to 0.230 μm in length. The interphase nuclei and prophase chromosomes of O. reheriana were categorized to be complex chromocenter type and interstitial type, respectively; the metaphase chromosome number of O. reheriana was reported 2n=2x=16, ranging from 1.15 μm to (0.468 μm) in length. These results can supply the cytological evidence for the further research on the biosystermatics and threatened mechanism of C. putoensis and O. reheriana two rare and threatened species of Betulaceae.