The application of this research was implemented at the laboratories of Food Science Department, Agriculture College, Damascus University in order to investigate the effect of different ratios of added oil upon the rheological, chemical and microbial characteristics of mayonnaise. The traditional mayonnaise was made from fresh egg, vinegar, salt, mustard, citric acid and corn oil at 70% ratio, to be used as a standard. Two changes in the oil ratio: 40% and 50% were applied for obtaining lower oil mayonnaise, with fewer calories (Diet). The influence of adding Xantan gum as a substitute to oil reduction, on the properties of final product was also investigated. Results showed that the addition of Xantan gum at 1.5% was necessary to complement the reduction in the added oil. The results also confirmed that reduction in the added oil of the diet mayonnaise led to reduction in viscosity and firmness when compared with the standard mayonnaise.