Herein, we investigated the possible roles of 13 core circadian clock genes in HCC, including ARNTL, CLOCK, CRY1, CRY2, DBP, NR1D1, NR1D2, NPAS2, PER1, PER2, PER3, RORA, and TIMELESS. The gene discussed is NPAS2; the disease is hepatocellular carcinoma.