We report Shubnikov-de Haas (SdH) oscillations of a three-dimensional (3D) Dirac semimetal candidate of layered material ZrTe5 single crystals through contactless electron spin resonance (ESR) measurements with the magnetic field up to 1.4 T.The ESR signals manifest remarkably anisotropic characteristics with respect to the direction of the magnetic field,indicating an anisotropic Fermi surface in ZrTe5.Further experiments demonstrate that the ZrTe5 single crystals have the signature of massless Dirac fermions with nontrivial 7π Berry phase,key evidence for 3D Dirac/Weyl fermions.Moreover,the onset of quantum oscillation of our ZrTe5 crystals revealed by the ESR can be derived down to 0.2 T,much smaller than the onset of SdH oscillation determined by conventionalmagnetoresistance measurements.Therefore,ESR measurement is a powerful tool to study the topologically nontrivial electronic structure in Dirac/Weyl semimetals and other topological materials with low bulk carrier density.