Epidemiologic studies indicate the use of either statins or aspirin have beneficial effects in prostate cancer patients. The present study was undertaken to evaluate the effects and mechanisms of atorvastatin and aspirin alone or in combination in human prostate cancer cells cultured in vitro and grown as xenograft tumors in severe combined immune-deficient (SCID) mice. The growth and apoptosis in prostate cancer cells were determined by the trypan blue exclusion and propidium iodide staining assays. Activation of the nuclear factor κB (NF-κB) was measured by luciferase reporter assay, and the levels of phospho-signal transducer and activator of transcription (Stat)3 and phospho-extracellular signal-regulated kinase (Erk)1/2 were determined by western blot analysis. Mice were injected subcutaneously with PC-3 cells in Matrigel. After 4-6 weeks, mice with PC-3 tumors received i.p. injections of vehicle, atorvastatin (5 mg/kg), aspirin (80 mg/kg), or atorvastatin (5 mg/kg) + aspirin (80 mg/kg) three times a week for 30 days. Our results demonstrated the combination of atorvastatin and aspirin had more potent effects on growth inhibition and apoptosis stimulation in prostate cancer cells than either drug alone. Mechanistic studies indicated the induction of apoptosis in PC-3 cells was associated with strong inhibition of NF-κB and decreases in the levels of phospho-Stat3 and phospho-Erk1/2. Results of the present study demonstrated a strong combined effect of atorvastatin and aspirin on inhibiting the growth of prostate cancer cells in vitro and in vivo. The findings provide a strong rationale for clinical evaluation of the combination of atorvastatin and aspirin in patients with prostate cancer.