MicroRNAs are emerging as important regulators of cancer-related pro-cesses. Our studies show that microRNA-9 (miR-9) is downregulated in human ovarian cancer relative to normal ovary, and overexpression of miR-9 suppresses cell growthin vitro. Furthermore, the 3¢-UTR of NF-jB1 mRNA is found to be regulated directly by miR-9, demonstrating that NF-jB1 is a functionally important target of miR-9 in ovarian cancer cells.