In this study, we aimed to develop and evaluate an effective system for nucleic acid delivery. For this purpose, shRNA-encoding plasmid against 5-alpha reductase (p5 alpha-Red) activity was selected as a model. In order to achieve the delivery of p5 alpha-Red and to obtain lower cytotoxicity, higher transfection and silencing efficiency, we developed solid lipid nanoparticles (SLNs) as a delivery vector by the melt-emulsification process. As a first step, microemulsions were prepared by using Compritol ATO 888 as internal oil phase; Tween 80 as a surfactant (S); ethanol as co-surfactant (CoS) and ultra-pure water as the continuous water phase. Then, obtained o/w microemulsion was dispersed in cold ultra-pure distilled water (0-4 degrees C) to form SLNs. The formulated nanoparticles were electrostatically bound to p5 alpha-Red to form SLN: p5 alpha-Red vectors. The SLN: p5 alpha-Red vectors have particle sizes of 62.65 nm, and zeta potential values of 12.9 mV. DNase I protection analysis showed that developed formulation is able to protect the p5 alpha-Red from degradation. The permeation study revealed that SLN: p5 alpha-Red vectors are able to pass the cellulose membrane and 80.2% of the SLN: p5 alpha-Red vectors were dialyzed after 6 h. According to cytotoxicity test results, no significant cytotoxicity was observed on DU-145 cells in the concentration range of 0.3-0.6 mu g/well. Furthermore, in vitro gene silencing experiment demonstrated that SLN: p5 alpha-Red vector effectively reduced 5 alpha-Red enzyme level 48 h after administration in DU-145 cell line. Considering the role of 5-alpha reductase in related diseases such as benign prostatic hyperplasia, androgenic alopecia and prostate cancer, the developed SLN: p5 alpha-Red vector system may have promises in future therapy.