Arabidopsis STABILIZED1 (STA1) encodes a protein that is homologous to human U5 snRNP-associated 102-kDa protein (PRPF6), and the yeast pre-mRNA splicing factors, PRP1p (fission yeast) and Prp6p (budding yeast), and is important in pre-mRNA splicing and mRNA stability. The pleiotropic defects of development, chilling sensitivity and hypersensitivity to ABA are observed in sta1-1, a weak allele of sta1. sta1-1, showing enhanced luminescence under cold stress, was originally isolated from a mutant pool generated with the bioluminescent plant harboring the stress-inducible RD29A promoter-driven luciferase gene (RD29A-LUC). Some developmental defects found in sta1-1 resembled those found in miRNA biogenesis mutants such as hyponastic leaves1-1 (hyl1-1) and serrate-1 (se-1). Similar to these miRNA biogenesis mutants, sta1-1 accumulated significantly lower levels of mature miRNAs and concurrently higher levels of pri-miRNAs than wild type. The dramatic reductions of mature miRNAs were associated with the accumulation of their target gene transcripts and the corresponding developmental defects. The reduction of miRNA accumulation in sta1-1 appeared to be because of the sta1-1 decfects in splicing of intron containing pri-miRNAs. In addition, sta1-1 decreased transcript levels of DICER-LIKE1 (DCL1) gene. These results suggest that STA1 is involved in miRNA biogenesis directly by functioning in pri-miRNA splicing and indirectly by modulating the DCL1 transcript level. Our efforts and recent findings to establish STA1-mediated RNA metabolism will be presented and discussed.