Purpose.To investigate the effects of Corbrin Capsule (CS-C-Q80), a drug derived fromCordyceps 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.