Objectives : Hypothyroidism is a relatively common endocrinologic disease, especially among older women. Western medical doctors treat hypothyroidism with levothyroxine, however there are several side effects, including thyrotoxicosis, atrial fibrillation, osteoporosis, etc. Therefore, traditional Korean medicine(TKM) offers an appealing alternative therapy for hypothyroidism. In this study, Cuscuta Semen was used to analyze its possible effect on a hypothyroidism rat model induced by propylthiouracil(PTU). Methods : 24 two-month-old Sprague-Dawley(SD) rats were divided into 4 groups: normal (n=6), PTU-induced hypothyroidism control(n=6), hypothyroidism rat treated with Cuscuta Semen (n=6), and hypothyroidism rat treated with levothyroxine(n=6). PTU was administered for 4 weeks, Cuscuta Semen and levothyroxine was administered 2 weeks after PTU was initiated for a total duration of 2 weeks. Blood samples from all the rats were taken from their hearts and analyzed. Results : When compared to the normal group, the PTU-induced control group showed significantly lower $T_4$, $T_3$ levels and significantly higher TSH level, which is indicative of hypothyroidism. The Cuscuta Semen group had significantly higher $T_4$ and significantly lower TSH than the control group(p<0.05). There was no significant difference in biochemical labs and weight between the Cuscuta Semen and control groups. Conclusions : These results suggest that Cuscuta Semen could be effective in increasing thyroid hormone production, and be powerful enough to affect the hypothalamus-pituitary-thyroid axis. Also, no adverse effects related with Cuscuta Semen were found, suggesting that it is relatively safe to administer. In conclusion, it seems that Cuscuta Semen is a safe alternative medicine for hypothyroidism.