Plants (just like other eukaryotes) have great diversity of RNA molecules that have essential and specific functions in cell and organism. Alongside coding mRNAs important function in gene expression have ncRNAs too, which include tRNAs, rRNAs, lncRNAs, snRNAs, snoRNAs, miRNAs, siRNAs and other sRNAs. Main topic of this paper are small RNAs (sRNAs), whose best investigated representatives are some ncRNAs: snRNAs, snoRNAs, miRNAs and siRNAs. miRNAs and siRNAs act in RNA silencing pathways, i. e. they reduce expression level of targeted genes in different conditions. In plants, silencing is usually executed on posttranscriptional level by targeted gene mRNA degrading. For activity of these sRNAs are required some proteins, in first place DCL enzymes, which cleave their precursors, and Argonaute enzymes, which are principal component of RISC complex and they degrade targeted complementary mRNAs. hcsiRNAs have specific role in regulation of gene expression on transcriptional level: targeted genes are silenced by RNA-directed DNA methylation (epigenetic regulation). Beside endogenous genes expression regulation, siRNAs and RNAi provide important defense mechanisms that protect plants from pathogens, especially from viruses, bacteria and fungi. In interaction of plants and their pathogens, pathogen responses on plant defense mechanisms are also present, both are changing and developing through time. Discoveries in the field of RNA silencing found application in developing of different methods for agricultural plant breeding