SUMMARYRCF1 is a highly conserved DEAD‐box RNA helicase found in yeast, plants, and mammals. Studies about the functions of RCF1 in plants are limited. Here, we uncovered the functions of RCF1 in Arabidopsis thaliana as a player in pri‐miRNA processing and splicing, as well as in pre‐mRNA splicing. A mutant with miRNA biogenesis defects was isolated, and the defect was traced to a recessive point mutation in RCF1 (rcf1‐4). We show that RCF1 promotes D‐body formation and facilitates the interaction between pri‐miRNAs and HYL1. Finally, we show that intron‐containing pri‐miRNAs and pre‐mRNAs exhibit a global splicing defect in rcf1‐4. Together, this work uncovers roles for RCF1 in miRNA biogenesis and RNA splicing in Arabidopsis.