RNA helicases regulate RNA metabolism, but their substrate specificity and in vivo function remain largely unknown. We isolated spontaneous mutant zebrafish that exhibit an abnormal dorsal bend at the beginning of tactile-evoked escape swimming. Similar behavioral defects were observed in zebrafish embryos treated with strychnine, which blocks glycine receptors (GlyRs), suggesting that the abnormal motor response in mutants may be attributable to a deficit in glycinergic synaptic transmission. We identified a missense mutation in the gene encoding RNA helicase Dhx37. In Dhx37 mutants, ribosomal RNA levels were unchanged, whereas GlyR α1, α3, and α4a subunit mRNA levels were decreased due to a splicing defect. We found that Dhx37 can interact with GlyR α1, α3, and α4a transcripts but not with the GlyR α2 subunit mRNA. Overexpression of GlyR α1, α3, or α4a subunits in Dhx37-deficient embryos restored normal behavior. Conversely, antisense-mediated knockdown of multiple GlyR α subunits in wild-type embryos was required to recapitulate the Dhx37 mutant phenotype. These results indicate that Dhx37 is specifically required for the biogenesis of a subset of GlyR α subunit mRNAs, thereby regulating glycinergic synaptic transmission and associated motor behaviors. To our knowledge, this is the first identification of pathologically relevant substrates for an RNA helicase.