The present study investigated the mechanism of Japanese apricot extract (JAE) in inhibiting lung cancer cells proliferation. JAE inhibited A549 lung cancer cell proliferation at non-cytotoxic doses and suppressed nuclear factor-${kappa}B$ (NF-${kappa}B$) activation induced by TNF-${alpha}$ at a dose of 1 mg/mL (p<0.05). Proteasome activities of A549 cells were blocked by JAE in a dose-dependent manner at concentrations of 0.67 and 1 mg/mL (p<0.05). These results indicate that JAE has anti-proliferative activity against A549 cells and suppresses NF-${kappa}B$ activation, partially due to inhibiting proteasome activity.