The effects of ultrasound on the molecular weight distribution and emulsifying properties of both xanthan gum (XG) and propylene glycol alginate (PGA) were investigated. The results showed that ultrasonic treatment at different intensities decreased the apparent viscosity and narrowed the molecular weight distribution. Higher intensity increased the effectivity of the sonochemical effect. Ultrasound degradation did not change the primary structure of the PGA-XG complex, and SEM analysis showed that the morphology of the original polysaccharide differed from that of the degraded polysaccharide fractions. The ultrasonic intensities and treatment times had a substantial influence on the stability of the polysaccharide-stabilized oil-in-water (O/W) emulsions. The O/W emulsion stabilized by the polysaccharide treated with 270 W ultrasound waves for 7 min led to the smallest average particle size (detected via fluorescence microscopy) and showed stability against aggregation in O/W emulsions.