Abstract Background In mammals, oocytes display compromised quality after experiencing a process of postovulatory aging. However, the mechanisms underlying are not yet fully understood. Here, we portrayed a protein expression profile of fresh and aging metaphase II (MII) mouse oocytes by means of four-dimensional label-free quantification mass spectrometry (4D-LFQ). Results The analysis of 4D-LFQ data illustrated that there were seventy-six differentially expressed proteins (DEPs) between two groups of MII stage oocytes. Fifty-three DEPs were up-regulated...