Plant extracts can have a significant role in the shelf-life prolongation of full-fat foods. So, the main objectives of the present study were to assess the effect of ethanolic chard leaves extract addition on the physicochemical, sensorial and microbiological mayonnaise properties. The ethanolic chard leaves extract was added to mayonnaise with levels 0.5. 1.0 and 1.5% of mayonnaise weight. Then, these samples were compared with mayonnaise samples fortified with tert-butyl hydroquinone (TBHQ) as the artificial antioxidant and with a sample without antioxidants as the control. The results displayed that the chard leaves had a high content of protein, ash and total phenolic content. The radical scavenging activity of ethanolic chard leaves extract was 90.11±1.21% compared to 95.22±0.87% for TBHQ at 120 min. An addition of chard leaves extract did not affect the chemical composition of mayonnaise. But it led to a shiny beige color and lost part of the polish appearance of samples. The mayonnaise containing 1.5% chard leaves extract had a non-significant decrease in most of the sensory evaluation scores, except the color, compared with the mayonnaise containing TBHQ and control. No significant differences in TBA values were observed between mayonnaise samples containing TBHQ and 1.5% chard leaves extract at different storing periods. Moreover, the TBA values, titratable acidity, the total bacterial, yeast and molds count increased in all mayonnaise treatments by progressing storage periods. Inversely, the viscosity and pH values decreased in all treatments by progressing storage periods. It can be recommended that the potentiality of using the extract of the chard leaves as a natural antioxidant during mayonnaise manufacture to delay oxidation and prolong the shelf-life of mayonnaise instead of chemical antioxidants.