Purpose: The therapeutic and anti-aging potential of mesenchymal stem cell secretome depends not only on its bioactive composition, but also on the preservation of its physicochemical and functional properties during downstream processing. Freeze-drying is widely used to enhance stability and shelf-life. However, suboptimal processing conditions may compromise structural integrity and bioactivity, thereby limiting its efficacy in skin regeneration and cosmetic applications. This study aimed to evaluate the effects of holding time and initial primary drying temperature on the physicochemical properties and biological activity of freeze-dried umbilical cord mesenchymal stem cell secretome (FD-UCMSCS). Methods: UC-MSCS samples were pre-frozen at − 80 °C for 6, 12, or 24 h and subsequently lyophilized under initial primary drying temperatures of − 25, −30, or − 35 °C. The resulting cakes were analyzed for macroscopic morphology, residual moisture, reconstitution time, pH, zeta potential, protein concentration and integrity. In vitro bioactivity was also evaluated by cytoprotection against H₂O₂ and wound closure on HaCaT cells. Results: Longer holding time (24 h) and lower primary drying temperature (− 35 °C) produced uniform cakes with minimal shrinkage, higher protein retention, and more negative zeta potentials (− 31 to − 63 mV), indicating improved colloidal stability. Despite partial protein loss, FD-UCMSCS maintained significant cytoprotective effects upon and accelerated wound closure, comparable to fresh secretome and positive control resveratrol. Conclusion: Optimized lyophilization conditions at 24 h holding time and − 35 °C primary drying temperature preserved both physicochemical integrity and biological activity of UC-MSCS, establishing a clear process–bioactivity correlation for developing stable, functionally active secretome formulations for therapeutic applications. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2026.