Th1/Th2 peripheral blood balance and CD200 expression in patients with severe alopecia areata (SAA) in the active stage were investigated. Fifty patients with active SAA, 50 patients with stable SAA and 50 healthy controls were continuously selected and expression of Th1/Th2 of peripheral T lymphocytes, and peripheral B lymphocytes was detected by flow cytometry; RT-PCR was used to detect the expression of the PBMC CD200 mRNA and the expression of CD200 in hair follicles of alopecia area was detected by immunohistochemically staining; ELISA was used to detect expression levels of serum LFN-γ and serum interleukin (IL)-10. The expression of CD200 in patients with alopecia areata in active phase on CD3+ T lymphocytes and CD19+ B lymphocytes was significantly lower (P<0.05) than those in stable phase and of the control group. CD200 expression in patients with alopecia areata in stable phase on T lymphocytes was greatly lower than that of the control group (P<0.05). However, the comparison of expression of CD200 in patients with alopecia areata in stable phase on B lymphocytes with the control group were statistically non-significant. The level of the expression of CD200 mRNA in active phase was obviously lower than those of the other two groups and the difference was statistically significant (P<0.05); the moderate positive and strong positive percentage of CD200 in the active phase was significantly lower than those of the other two groups. Positive expression rate of CK15 among the three groups were compared with each other; the differences had no statistical significance. The level of LFN-γ in the active phase had obviously increased while the IL-10 level decreased significantly (P<0.05). In conclusion, the level of expression of CD200 on peripheral blood and hair follicle outer root sheath of patients with SAA was decreased. This may be associated with the imbalance of the Th1/Th2 equilibrium.