Objective To investigate the circadian rhythm of peripheral blood cell counts in Chinese healthy volunteers and nasopharyngeal carcinoma patients. Methods A total of 13 nasopharyngeal carcinoma patients and 14 healthy volunteers were enrolled in this study. Venous blood was sampled every 4 hours during a 24-hour period. EDTA anticoagulated whole-blood was tested for blood cell counts immediately by automated hematology analyzer. The plasma cortisol level was determined by Radioimmunoassay. Data were analyzed by Analysis of Variance for Repeated Measures using SPSS 13.0 software and by Cosinor Analysis using Cosinor Analysis Software. Results Both healthy volunteers and nasopharyngeal carcinoma patients displayed clear circadian rhythms in red blood cells, hemoglobin, leukocytes, lymphocytes, and possibly platelets. Those blood cell counts also showed a significant variation during 24h. Conclusion Peripheral blood cell counts display significant circadian rhythms in both healthy volunteers and advanced nasopharyngeal carcinoma patients, suggesting the possibility of performing the time-selective collection and transfusion of blood.