Hypoxia-inducible factor 1 (HIF-1), a transcription factor that is critical for tumor adaptation to microenvironmental stimuli, represents an attractive chemotherapeutic target. YC-1 is a novel antitumor agent that inhibits HIF-1 through previously unexplained mechanisms. In the present study, YC-1 was found to prevent HIF-1α and HIF-1β accumulation in response to hypoxia or mitogen treatment in PC-3 prostate cancer cells. Neither HIF-1α protein half-life nor mRNA level was affected by YC-1. However, YC-1 was found to suppress the PI3K/Akt/mTOR/4E-BP pathway, which serves to regulate HIF-1α expression at the translational step. We demonstrated that YC-1 also inhibited hypoxia-induced activation of nuclear factor (NF)-κB, a downstream target of Akt. Two modulators of the Akt/NF-κB pathway, caffeic acid phenethyl ester and evodiamine, were observed to decrease HIF-1α expression. Additionally, overexpression of NF-κB partly reversed the ability of wortmannin to inhibit HIF-1α-dependent transcriptional activity, suggesting that NF-κB contributes to Akt-mediated HIF-1α accumulation during hypoxia. Overall, we identify a potential molecular mechanism whereby YC-1 serves to reduce HIF-1 expression.