Emulsifiers are used in various industries, and the functional development of these emulsifiers is necessary. The objective of this study was to determine the effect of addition of 1-monocaprin on the emulsion stability and viscosity of mayonnaise as an index of storage stability. Mayonnaise made of soybean oil, egg yolk, sugar, salt, and vinegar was supplemented with 20, 40, 60, 80, and 100 ppm of 1-monocaprin. The effects of 1-monocaprin addition on storage stability and emulsion stability of mayonnaise were determined by observing changes in the average $Delta$-backscattering flux (%) after storage at $60^{circ}C$ for 24 hr. The viscosity of each sample was also measured. Mayonnaise containing 60 ppm of 1-monocaprin had the highest emulsion stability followed in order by mayonnaise containing 40, 20, 80, and 100 ppm 1-monocaprin. Analysis showed that apparent viscosity decreased at a slower rate with higher 1-monocaprin concentrations. From the above results, it could be concluded that the optimal concentration of 1-monocaprin added to mayonnaise for the emulsion stability and the storage stability was 60 ppm.