This study aimed to use the biocompatibility features of the biodegradable polymers to prepare depot injectable finasteride (FIN) microspheres for the treatment of benign prostatic hyperplasia. FIN microspheres were prepared utilising an emulsion-solvent evaporation/extraction technique. The Box-Behnken experimental design was adopted to optimise the preparation process. FIN plasma levels in albino rabbits were determined after injection with optimised FIN microspheres formula and compared with oral FIN suspension. Results revealed that the optimum microspheres displayed an amended sustained release pattern with lower initial burst. The cumulative FIN % released after 25 days was in the range 27.83-73.18% for F-4 and F-1, respectively. The optimised formula, with 50.0% (X-1), and 22.316% (X-2) and 1.38% (X-3) showed 6.503m, 93.213%, 14.574%, and 64.838% for Y-1, Y-2, Y-3, and Y-4, respectively. In vivo studies displayed a sustained release pattern with minimal initial burst release when injected into rabbits.