BACKGROUND:Umbilical cord-derived mesenchymal stem cel s are gaining more attention in clinical treatments. Cel viability prior to transplantation has a direct impact on clinical prognosis. Despite trypan blue staining is a widely performed procedure to assess the viability of umbilical cord-derived mesenchymal stem cel s, it cannot reflect the functional capacity of those cel s accurately because of some subjective factors. OBJECTIVE:To explore sensitive and accurate assay for the functions of umbilical cord-derived mesenchymal stem cel s. METHODS:Human umbilical cord-derived mesenchymal stem cel s were isolated and cultured in vitro. Cultured umbilical cord-derived mesenchymal stem cel s were preserved in 0.9%saline for 0, 2, 4 and 6 hours at 4 ℃. Various methods (trypan blue staining, AnnexinV-PI, terminal deoxynucleotidyl transferase dutp nick end labeling, cel counting kit-8, live-dead assay, cel adherent assay) were used to determine the viability of post-storage umbilical cord-derived mesenchymal stem cel s, and the results were compared with colony-forming efficiency, a measure of cel function. RESULTS AND CONCLUSION:Human umbilical cord-derived mesenchymal stem cel s cultured in vitro showed a spindle shape and attached growth, the third-generation umbilical cord-derived mesenchymal stem cel s were positive for CD29, CD44, CD105, and negative for CD 34 and CD 45. Umbilical cord-derived mesenchymal stem cel s incubated in the adipogenic and osteogenic medium were both positive. Cel viability measured with trypan blue correlated moderately with colony-forming efficiency, while the percentage of viable cel s measured with other methods correlated better with colony-forming efficiency, among which adherent assay was the most obvious. It is proved that cel adherent assay-measured viability is the most accurate indicator.