Abstract: The effects of addition of two formulated herbal traditional Chinese medicines (TCM) in feed on serum NO and activities of NOS and iNOS of weaned piglets were investigated. TCM I was formulated to contain 10% Houttuynia cordata Thunb., 20% Astragalus membranaceus, 15% Poria cocos, 10% Acanthopanax senticosus, 15% Crataegus pinnatifida Bunge, 10% Angelica sinensis, 10% Magnolia officinalis and 10% Dianthus superbus, whereas TCM Ⅱ, 10% Lonicera japonica Thunb., 20% Astragalus membranaceus, 15% P. cocos, 10% A. senticosus, 15% C. pinnatifida Bunge, 10% A. sinensis, 10% M. officinalis and 10% D. superbus. From 16 litters (about 9 heads per litter) of similar parity and age, the breastfeeding piglets were randomly divided into four groups, namely the TCM Group Ⅰ, TCM Group Ⅱ, Antibiotics Group and Control. TCM I at 4 kg·t^-1, TCM Ⅱ at 4 kg·t^-1, chlortetracycline at 70 kg·t^-1 or bacitracin zinc at 30 kg·t^-1 was added to a same basal diet for the treatment groups. Blood samples of the piglets were taken at 1, 4, 7, 14 and 28 days after weaning to determine the serum NO and activities of NOS and iNOS. The contents of NO in TCM Group Ⅰ and Ⅱ piglets increased by 65.75% and 56.05%, respectively, as compared to Control (P < 0.05). After weaning for 28 days, the activity of NOS of piglets in TCM Group Ⅰ was 17% and that of TCM Group Ⅱ, 16.89%, higher than Control (P < 0.05). One day after weaning, the activity of iNOS in piglets in TCM Group Ⅰ decreased 6.4% in comparison to Antibiotics Group (P > 0.05) and declined 10% over Control (P > 0.05), while that of TCM Group Ⅱ decreased 6.5% over Control (P > 0.05). The results indicated that the TCMs could increase serum NO and NOS activity and reduce iNOS activity protecting the gastrointestinal mucosa in weaned piglets. The addition effectively alleviated weaning stress on the piglets suggesting a potential for the TCMs to replace antibiotics administration for the purpose.