Purpose: To investigate the effects of bortezomib alone and in combination with 5-fluorouracil (5-FU) on proliferation and apoptosis in the human choriocarcinoma cell line JEG-3. Materials and Methods: Cells were treated with bortezomib, 5-FU or with a combination. Proliferation and apoptosis were measured. NF-κB protein expression was examined using immunofluorescence. Results: Following treatment with ten nM bortezomib, rates of apoptosis were significantly higher than controls (p < 0.05) and NF-κB expression increased. 5-FU at 0.025 μg/ml or 0.25 μg/ml resulted in 60.1 ± 0.4% and 67.0 ± 0.2% growth inhibition, respectively, an increase compared to individual treatment (p < 0.05). Apoptosis in cells treated with bortezomib +5-FU was significantly higher than either treatment alone (p < 0.05). Inhibition of proliferation by the combination treatment was synergistic. Conclusion: Bortezomib alone or in combination with 5-FU inhibited JEG-3 cell proliferation and induced apoptosis by increasing NF-κB expression. Combination treatment exerted synergistic effects on growth inhibition.