Purpose. To investigate the effects of Corbrin Capsule (CS-C-Q80), a drug derived from Cordyceps sinensis (Berk.) Sacc., on autoimmune thyroid diseases (AITD). Methods. 44 Patients with Graves’s disease (GD) and 56 patients with Hashimoto’s thyroiditis (HT) were randomly assigned to treatment group (GD-Tx and HT-Tx) or control group (GD-Ct and HT-Ct). The control groups were given methimazole or levothyroxine only while the treatment groups were given Corbrin Capsule (2.0 g tid) besides the same conventional prescriptions as control groups. Thyroid hormones, thyroid antibodies, and T lymphocyte subsets were quantified at baseline and 24 weeks posttreatment. Results. Significant drop of serum anti-TPO-Ab levels was observed in both GD-Tx and HT-Tx groups. Before treatment, GD patients had higher helper T cells compared to cytotoxic T cells, while HT patients suffered from a nearly inverted proportion of helper T/cytotoxic T cells. There was a significant drop of the helper T/cytotoxic T cells ratio in GD-Tx to the median of the normal ranges after Corbrin treatment for 24 weeks, while that in HT-Tx was elevated. Conclusion. Corbrin Capsule could restore the balance between helper T and cytotoxic T cells in both GD and HT patients with dual-directional immunomodulatory effects. And it could significantly reduce the autoantibody levels in both GD and HT.