MicroRNAs are arising as the next generation of diagnostic and therapeutic tools for gene silencing. Studies demonstrated that the miR-29 expression is decreased in Alzheimer's disease (AD) patients displaying high levels of human β-secretase (hBACE1). Recent advances toward an effective therapy for AD intend to employ miR-29 to suppress hBACE1 expression and subsequent Amyloid-β (Aβ) peptide. However, delivery of mature miRNA has demonstrated modest efficacy in vitro; therefore, the preparation of highly pure and biologically active pre-miRNA arises as one of the most important challenges in the development of these therapeutic strategies. Recently, we described a new strategy based arginine-affinity chromatography to specifically purify the recombinant pre-miR-29b. Following this strategy, the purified pre-miR-29b was successfully encapsulated into polyplexes that were further delivered in cytoplasm. It was verified that Chitosan/pre-miR-29b and Polyethylenimine/pre-miR-29b systems efficiently delivered pre-miR-29b to N2a695 cells, thus reducing the hBACE1 protein expression (around 78% and 86%, respectively) and Aβ42 levels (approximately 44% and 47%, respectively). Furthermore, pre-miR-29b downregulates the hBACE1 mRNA expression in 80%. Overall, it was demonstrated that the recombinant pre-miR-29b using polyplexes allowed to decrease the hBACE1 and Aβ42 expression levels, improving the currently available methodologies of miRNA-based therapeutics.