Purpose: Nonsteroidal anti-inflammatory agents may inhibit carcinogenesis in specific tissues including the colon, breast, and pancreas, and, hence, may prove to be effective chemopreventive agents. The purpose of this study was to investigate the cellular effects of acetylsalicylic acid (ASA), acetaminophen, and a COX-2 inhibitor (NS-398) on the growth of cell lines of human ovarian cancer in vitro. Experimental Design: SK-OV-3, Caov-3, and NIH-OVCAR-3 ovarian carcinoma cell lines were treated with ASA (10-6 M-10-2 M), acetaminophen (10-6 M-10-2 M), and a COX-2 inhibitor (10-6 M-10-4 M) for 96 h. The number of viable cells was determined using a tetrazolium conversion assay. Immunohistochemical assessment was performed for alterations in expression of Ki-67, erbB-2, COX enzyme, and apoptosis in primary ovarian cancer cells using terminal deoxynucleotidyl transferase (Tdt)-mediated nick end labeling assay. Results: A decrease in cell number compared with controls was observed for all of the cell lines treated with ASA, acetaminophen, and COX-2 inhibitor by cell count and tetrazolium conversion assay. A significant decrease in Ki-67 compared with controls in the OVCAR-3 (P = 0.005) and SK-OV-3 (P = 0.007) cell lines after treatment with the COX-2 inhibitor was observed. We observed a decrease in mitotic activity compared with controls in each cell line after treatment with the COX-2 inhibitor. Apoptosis was observed in primary ovarian cancer cell culture treated with COX-2 inhibitor. Conclusion: Our results suggest additional study for the use of nonsteroidal anti-inflammatory agents, specifically COX-2 inhibitors, as a strategy of chemoprevention for ovarian cancer.