Accumulating data suggest that micro RNAs (miRNAs) or double-stranded RNAs (dsRNAs) can activate gene expression by targeting promoters. The cyclin-dependent kinase inhibitor p21(CIP1/WAF1) (p21) has also been shown to suppress epithelial-mesenchymal transition (EMT) which plays a crucial role in the early stage of tumor metastases and invasiveness. In a previous study, we have reported that miR-370-5p is low-expressed in bladder cancer (BCa) tissues and cell lines. Here, we identified that miR-370-5p and sequence homology dsRNA (dsP21-555) fully complementary to promoter hold the potent abilities to induce p21 expression. Moreover, transfection of miR-370-5p or dsP21-555 into BCa cells remarkably inverts EMT-associated genes (increases epithelial cell makers E-cadherin and beta-catenin, and decreases mesenchymal cell markers ZEB1 and Vimentin) expression mainly via regulating p21 expression. Besides, through manipulating p21, both the candidates can retard BCa cell migration and invasion. In summary, our results provide evidence that both endogenous and exogenous small RNAs may function to induce p21 expression by interacting with the similar promoter region and impede BCa metastasis.