Objective : Acupuncture has been used for treatment of numerous disorders, especially for pain control in Oriental Medicine. However, the mechanism of pain control by acupuncture was not clear until now. This study was performed to prove analgesic mechanism of acupuncture treatment at acupoint $ST_{36}$ by observing the changes of abdominal pain and c-Fos expression in the thalamus. Methods : Abdominal pain was induced by acetic acid, and the changes of writhing reflex after acupuncture treatment on $ST_{36}$ and non-acupoints were measured. c-Fos immunohistochemistry was also performed to study the changes of the neuronal activity in the thalamus. Results : The writhing reflex decrease significantly after acupuncturing at $ST_{36}$ compared with control group(p<0.05). The changes of the writhing reflex by non-acupoint acupuncture treatment also showed significant decrease compared with control group(p<0.05). c-Fos expression in the thalamus, especially periventricular part was significantly decreased after acupuncturing as $ST_{36}$ compared with control groups(p<0.05). Conclusion : This study shows that the acupuncture has the analgesic effect in the abdominal pain induced by acetic acid and the thalamus might be a important area for this mechanism.