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This study investigates the effect of adding nano-extract of the watercress on the properties of soy polysaccharide films. To achieve this, the extract of the watercress was obtained using the ultrasonication method, and the amounts of phenolic compounds and anti-microbial activity (against the Gram-negative bacterium Escherichia coli and the Gram-positive bacterium Staphylococcus aureus) in the extract were measured. For the purpose of encapsulating the extract, maltodextrin-nanoprotein concentrate from whey was utilized. Subsequently, different concentrations of the extract and nano-extract (500 and 1000 ppm) were added to soy polysaccharide films, and the physical, mechanical, and anti-microbial properties of the produced films were studied. The results indicated that the watercress extract contains significant amounts of phenolic compounds and exhibits high anti-microbial properties. Seven compounds (99.12%) were identified, with the highest amounts attributed to Quercetin (41.36%), Gallic acid (23.33%), and Ferrullic acid (18.18%). Film properties revealed that the addition of the extract generally improved film characteristics, reducing moisture content, solubility, and water vapor permeability, while increasing tensile strength. Additionally, substituting nano-extract for the extract also enhanced film properties in most cases. Soy polysaccharide films containing the extract demonstrated strong anti-microbial properties against pathogenic bacteria, with an increase in anti-microbial activity as the concentration rose and the extract transformed into nano-extract. Consequently, soy polysaccharide films with watercress nano-extract at a concentration of 1000 ppm can be utilized as a preservative in food packaging due to their anti-microbial properties. [ABSTRACT FROM AUTHOR]