Small proteins are ubiquitous in cells and are conserved in many species. With advances in genome sequencing technology and computational biology, more and more evidence indicate that small proteins perform important functions and participate in stress responses in both prokaryotes and eukaryotes. However, the mechanism of small proteins regulate stress response is unclearly. In this study we found an unknown function small protein Cmi7p rapidly reacted to acetic acid stress and increased its expression. Further study found that Cmi7p affected cell cycle process and increased the efficiency of cell division under stress.