MicroRNAs (miRNAs) play an essential role in cancer therapy, but the disadvantages of its poor inherent stability, rapid clearance, and low delivery efficiency affect the therapeutic efficiency. Loading miRNAs by nanoformulations can improve their bioavailability and enhance therapeutic efficiency, which is an effective miRNA delivery strategy. In this study, we synthesized layered double hydroxides (LDH), which are widely used as carriers of drugs or genes due to the characteristics of good biocompatibility, high loading capacity, and pH sensitivity. We loaded the suppressor oncogene miR-30a on LDH nanomaterials (LDH@miR-30a) and determined the mass ratio of miRNA binding to LDH by agarose gel electrophoresis. LDH@miR-30a was able to escape the lysosomal pathway and was successfully phagocytosed by breast cancer SKBR3 cells and remained detectable in the cells after 24 h of co-incubation. In vitro experiments showed that LDH@miR-30a-treated SKBR3 cells showed decreased proliferation and cell cycle arrest in the G0/G1 phase and LDH@miR-30a was able to regulate the epithelial-mesenchymal transition (EMT) process and inhibit cell migration and invasion by targeting SNAI1. Meanwhile, in vivo experiments showed that nude mice treated with LDH@miR-30a showed a significant reduction in their solid tumors and no significant impairment of vital organs was observed. In conclusion, LDH@miR-30a is an effective drug delivery system for the treatment of breast cancer.