Abstract: 【OBJECTIVE】The angiotensin converting enzyme (ACE) inhibiting activity of four kinds of Lactobacillus helveticus fermented milk whey was determined in this paper, and their effects on blood pressure were investigated using spontaneously hypertensive rats.【METHODS】 The ACE inhibitory activity was measured according to the method of Cushman and Cheung with some modification. The effects of Lactobacillus helveticus fermented milk whey, water, and skim milk on blood pressure was evaluated in 8-week-old spontaneously hypertensive rats (SHR) weighing 180-200 g. Every sample was used to SHR on consecutive three days, during which they received increasing doses by gastric intubation. The systolic blood pressure was measured by ZH-HX-Z tail cuff with a programmed electro-sphygmomanometer .【RESULTS】Lactobacillus helveticus TUST005 showed higher ACE inhibitory activity than others, and the highest inhibitory activity of the fermented milk stored at 4℃ for three days reached 45.91%. At 15 mL per kg body weight dose of Lactobacillus helveticus TUST005 and Streptococcus diacetilactis fermented milk whey and the 20 mL per kg body weight dose of Lactobacillus helveticus TUST005 fermented milk whey. we observed a marked and long-lasting hypotensive effect for 6 hours. The maximum decrease in mean arterial blood pressure (20.2 mmHg) was achieved. 【CONCLUSION】The results indicate that there is a good correlation between in vivo and in vitro datas for the Lactobacillus helveticus TUST005 fermented milk.