(1) Background: Blackberry seed oil (BSO), obtained from Rubus spp. Xavante cultivar via supercritical CO₂ extraction, contains bioactive lipids and antioxidants, but its cosmetic application is limited by poor solubility and stability. Nanoencapsulation with poly(ε-caprolactone) (PCL) can overcome these limitations. (2) Methods: BSO was characterized by UHPLC–ESI–Q-TOF–MS and incorporated into PCL nanocapsules (NCBSO) using the preformed polymer deposition method. Physicochemical properties, stability (at 4 °C, room temperature, and 37 °C for 90 days), cytotoxicity, and collagen production were assessed in human fibroblasts. (3) Results: NCBSO showed nanometric size (~267 nm), low polydispersity (PDI < 0.2), negative zeta potential (−28 mV), and spherical morphology confirmed by FE-SEM. The dispersion remained stable across all tested temperatures, preserving pH and colloidal properties. In particular, BSO and NCBSO at 100 µg.mL-1 significantly enhanced collagen production by 170% and 200%, respectively, compared to untreated cells (p < 0.01). Superior bioactivity was observed for NCBSO. No cytotoxic effects were achieved. (4) Conclusions: The nanoencapsulation of BSO into PCL nanocapsules ensured formulation stability and potentiated collagen production. NCBSO may be further used as a novel cosmeceutical for collagen-boosting skincare.