Abstract We examined variation of some hormones reflecting reproductive function in the blood plasma of red-bellied squirrels (Callosciurus erythraeus). 70 males and 74 females were captured from February to December 2015 from Yingjing County, Sichuan Province. We measured the levels of reproductive hormones (testosterone: T, estradiol: E2, follicle-stimulating hormone: FSH, luteinizing hormone: LH, gonadotropin-releasing hormone: GnRH, progesterone: P4) by ELISA, and analyzed the data from the different sexes and months. In addition, impacts of reproductive status were also analyzed. These indices were analyzed by two-way ANOVA or ANCOVA. If some indices showed significant sex differences, monthly variations of those indices for any gender were further examined by one-way ANOVA or ANCOVA. The results were as follows: （1）There were sex differences in the levels of serum reproductive hormones in female and male squirrels that changing with reproductive status (except GnRH), and were lowest in October. （2）The serum concentrations of FSH, LH, T, E2 and P4 in males peaked in February or March and July or August, shortly before mating. Concentrations of FSH, LH and E2 in females and GnRH of both sexes peaked in February and July during the mating period, whereas T concentrations in females were low throughout the year, and serum P4 was highest in May. （3）Compared with non-reproductive squirrels, the concentrations of all serum reproductive hormones were significantly higher in pregnancy, mating and lactating female squirrels, or mating males. These results indicate that the levels of serum reproductive hormones in female and male squirrels can vary with the seasons and the reproductive status, which is of great significance to understanding the reproductive characteristics of the red-bellied squirrels and control their damage to plantations.