Atractylenolide I, an active sesquiterpene component extracted from Rhizoma atractylodis, inhibits T24 bladder cancer cell proliferation by arresting the cell cycle in the G2/M phase via downregulation of cell cycle-related proteins such as CDK1, cell division cycle 25C (CDC25c), and cyclin B1. Here, CDK1 is linked to urinary bladder cancer.