Objective To observe the seasonal change of Clock gene expression in blood lymphocytes in rats model with defensive-qi deficiency. Methods Twenty Sprague Dawley rats were randomly and equally assigned into control and model groups one week before spring equinox

summer solstice

autumnal equinox and winter solstice.Rats in control group were fed routinely

while those in model group were dealt with methods combining fatigue with alternate cold and heat stimulation to establish defensive-qi deficiency model. Clock gene expressions in blood lymphocytes in rats of both groups were measured one week later in each solar term by RT-PCR. Results Expressions of Clock gene were significantly decreased in model group than those in control group in each corresponding solar term（ P < 0. 05）. Compared within the same group

Clock gene expressions were significantly lower in summer solstice

autumnal equinox and winter solstice than that in spring solstice（ P < 0. 05）. It was significantly lower in winter solstice than those in summer solstice and autumnal equinox（ P < 0. 05）. However

there was no significant difference in Clock gene expression between summer solstice and autumnal equinox（ P > 0. 05）. Conclusion Clock gene expression in blood lymphocytes in rats with defensive-qi deficiency exhibits seasonal changes including higher in spring equinox and lower in winter solstice. These changes are in accordance with those in normal rats.