Sambucus nigra L. is a well-known species with a wide range of medicinal properties. In this work, supercritical fluid extracts were obtained from fresh and dried elderberries of S. nigra L.: A (dried berries, ethanol (C₂H₅OH) absolute), B (dried berries, ethanol 96%), C (dried berries, ethanol 70%) and D (fresh berries, ethanol 96%). Evaluation of the in vitro enzymatic activities and antioxidant activity (AA) of the extracts and a preliminary assessment of their safety were carried out. The most promising extracts were selected for encapsulation in polymeric nanoparticles (NPs). All extracts demonstrated low to moderate AA, and they did not reveal any antimicrobial activity against the bacteria and yeasts tested. No toxic effect in the Artemia salina model was observed. Due to the moderate or good AA, anti-collagenase and anti-elastase activities, A and C extracts were selected and then successfully encapsulated into poly(lactide-co-glycolide) (PLGA) NPs. According to morphological analysis, empty PLGA NPs had a rounded irregular shape and seemed somewhat collapsed, while PLGA NPs loaded with extract A or C exhibited a spherical shape with a smooth surface. The encapsulation process produced a slight increase in the NP size. Further studies will include the optimization of extract conditions in order to improve the yield of extraction, as well as the in vivo evaluation of these nanocarriers.