In this study, muscle-derived stem cell (MDSC)/Pluronics/polycaprolactone (PCL) microparticle hybrid mixture was prepared as a potential injectable urethral bulking agent for the treatment of urinary incontinence. The MDSCs were isolated from the gastrocnemius muscles of SD rats by a modified preplate method and characterized through FACS analysis using various primary antibodies (CD34, Sca-1, CD45 and desmin). The hybrid mixture was prepared by the mixing of PCL microparticles (diameter, 100~200 μm) and MDSCs-containing thermo-sensitive Pluronic (F127/F68 mixture) solution (4.5/5.5, w/v). The hybrid mixture was easily injected through 18G needle into the body and stably remained in the applied site without initial volume decrease, owing to a well-packed structure of PCL particles exhibited in the hybrid mixture. It was observed that the MDSCs were stably grown in the hybrid mixture without severe inflammation and immune reaction. From the results, we recognized that the hybrid mixture can be a good candidate as an injectable bulking agent for the treatment of urinary incontinence, due to their good injectability, volume retention and biocompatibility.