Abstract: For studying the endocrine mechanism about seasonal empathema of Jining Gray goats, the principle of the melatonin concentration in peripheral blood and serotonin contents in pineal body were tested by radioimmunoassay and immunohistochemistry in vernal equinox, summer solstice, autumnal equinox and winter solstice. The results indicated that the concentration of melatonin showed circadian rhythm in peripheral blood, it reached the maximum at midnight and minimum at midday. Melatonin contents associated with seasonal changes. At night, the average concentration of melatonin in the summer solstice was the highest (P<0.01), no difference between the vernal equinox and the autumn equinox (P>0.05), and the concentration of melatonin in this three seasons were significant higher than that in the winter solstice (P<0.05).At daytime, melatonin contents showed no difference in all seasons (P>0.05). The area of serotonin-positive cells was the smallest in summer, the largest in winter in pineal body. There were no significant difference between spring and autumn (P>0.05).