Soy protein isolate (SPI) is known to reduce the risk of heart disease by lowering serum cholesterol and triacylglycerol (TG) levels. Soybean β-conglycinin, which is a component of SPI, might be the active ingredient that prevents and/or ameliorates lifestyle-related diseases, such as hyperlipidemia and obesity. This study aimed to determine the efficacy of soybean β-conglycinin for lowering the human serum TG level and visceral fat. Randomized double-blind placebo-controlled designs were used to test the effect of dietary β-conglycinin, which was taken in the form of candy. [Test 1]In order to examine the serum TG level, 138 volunteers aged 26 to 69 years with TG concentrations above 1.69 mmol/L participated in the study. The subjects were divided at random into two different groups: the test group only consumed the experimental candy containing β-conglycinin and the placebo group only consumed the placebo candy containing casein. The test period consisted of a 2-wk pre-evaluation phase to screen the participants, a 12-wk consumption period and a 4-wk post-evaluation phase. The serum TG concentrations were significantly reduced in the test group, compared with the placebo group, after consuming the experimental candy. [Test 2]In order to measure visceral fat by means of CT scanning, 102 volunteers aged 26 to 69 years with body mass indices (BMI) between 25 and 30 participated in the study. The subjects were divided at random into two different groups as for Test 1. The test period consisted of a 2-wk pre-evaluation phase to screen the participants, a 20-wk consumption period and a 4-wk post-evaluation phase. A significant reduction in visceral fat only occurred in the β-conglycinin group. This study showed that β-conglycinin is an effective food ingredient that will be of use to reduce high serum TG concentrations and to prevent obesity.