Rapid progress has been made regarding the understanding of brassinosteroid (BR) signaling in Arabidopsis. However, little is known about BR signaling in monotyledons. Here, we characterized a ricedwarf and low-tillering(dlt) mutant and cloned the corresponding gene via map-based cloning.DLTencodes a new member of the plant-specific GRAS family. The dwarf phenotype ofdltis similar to BR-deficient or signaling mutants in rice. In addition, both lamina bending and coleoptile elongation assays show thatdltis insensitive or much less responsive to brassinolide (BL), the most active BR, suggesting that DLT is involved in BR signaling. Consistent with this conclusion, the accumulation of transcripts of BR biosynthesis genes in thedltmutant indicated that DLT is involved in feedback inhibition of BR biosynthesis genes. In addition, transcription of several other BR-regulated genes is altered in thedltmutant. Finally, consistent with the fact thatDLTis also negatively feedback-regulated by BR treatment, a gel mobility shift assay showed that OsBZR1 can bind to theDLTpromoter through the BR-response element. Taken together, these studies have enabled us to identify a new signaling component that is involved in several specific BR responses in rice.