Single particle electron cryo-microscopy (cryo-EM) of RNA alone has not been studied at high resolution as in the case of RNA-protein complexes, because of the intrinsic conformational variability that presents great challenges in particle classification for high resolution structure determination. T-box riboswitches interact with specific tRNAs and sense the corresponding amino acid levels in Gram-positive bacteria. The complete structure of the T-box/tRNA (80 kDa) complex remains unknown. We here report a subnanometer cryo-EM map of this RNA complex, in which major and minor grooves are unambiguously resolved. This result differs from the two small angle X-ray scattering (SAXS) models reported recently, and illustrates the interaction interface between tRNA and T-box riboswitch.