We, for the first time, studied circadian expression of PER1 in buccal squamous cell carcinoma cells, which demonstrated that PER1 mRNA expression had circadian rhythm, with peak value occurred in middle to late activity phase (19.48 HALO), trough value in middle rest phase (7.64 HALO), showing a approximate 3.81-fold peak-to-trough variation. The gene discussed is PER1; the disease is squamous cell carcinoma.