Exon array, Western blot, real-time polymerase chain reaction (PCR), and luciferase report analyses have revealed that miR P-27-5p targets CDK4. Our observations indicate that miR P-27-5p inhibits cancer cell proliferation and triggers G1 cell cycle arrest by targeting CDK4 and suppressing phosphorylation of RB1. The gene discussed is CDK4; the disease is cancer.