Abstract: Unbalanced consumption of fat-rich foods tends to increase high risk of chronic diseases and death. A promising way is to create reduced-fat and fat-free products to solve the problems. However, the reduction of fat content normally can cause some changes, such as undesired texture, in food production. This study aims to investigate the aggregation behavior of alginate (Alg) sodium and egg yolk proteins under acidic pH conditions, and further to design a sort of low-fat mayonnaise products based on the aggregation mechanism. All low-fat mayonnaise products showed 30% oil phase fraction, and some significant properties of high viscoelasticity and thixotropy. A high fat mayonnaise with 75% oil phase fraction was used as a control. The results show that when the pH value was lower than 5.0, Alg carried negative charges but the dispersion of egg yolk carried positive charges, indicating that an obvious electrostatic aggregation occurred between Alg and egg yolk proteins. The structural strength of the mixture system of Alg and egg yolk significantly increased in this case. The Confocal laser scanning microscope (CLSM) results showed that Alg and egg yolk has formed aggregates at the pH value lower than 5.0. However, there was no any aggregates to be observed when the pH value was higher than 5.0. It was also found that addition amounts of white vinegar (0-10 mL, at a fixed total volume of 100 mL mayonnaise product) can determine the structuralized process in the low-fat mayonnaise products. The reason can be explained by the fact that the vinegar addition can decrease the pH value in the mayonnaise system, and thereby lead to the electrostatic attraction between Alg and egg yolk proteins. When the amount of white vinegar was higher than 2% (v/v), the pH value of the mayonnaise decreased to below 5.0, indicating that white vinegar can induce the electrostatic aggregation effect of the mayonnaise, thereby to increase the structural strength of products. With the increase in the addition amount of white vinegar, the aggregation effect was much more significant, and the structural degree was much higher than before in the low-fat mayonnaise products. In addition, the structural mechanism of the mayonnaise products can be that, the egg yolk-stabilized emulsion was dispersed into the mayonnaise systems, where the aggregates of egg yolk proteins and Alg acted as the continuous phase to confer the mayonnaise with significant viscoelasticity and thixotropy. Further investigations showed that the thermal stability of the low-fat mayonnaise products was affected by the addition amount of white vinegar. Good freeze-thaw stability can be achieved in all mayonnaise products, whereas the excessive addition of white vinegar can reduce the thermal stability of the low-fat mayonnaise products. The over addition of white vinegar can also decrease the flavor and sensory acceptability of the mayonnaise products. The rheological properties of the prepared low-fat mayonnaise product were close to those of the control group, and the sensory acceptability reached the highest, when the addition amount of white vinegar was 4% (pH value 4.6). Compared with the high fat mayonnaise (control), the low-fat mayonnaise demonstrated the similar texture but contained less fat. This finding can provide a novel and facile approach to develop the promising reduced-fat food products.