Dielectric tensor tomography (DTT) is a holographic technique for reconstructing three-dimensional (3D) dielectric tensors, providing a physical quantity of optical anisotropy. In this study, we introduce a cost-effective and robust DTT method that utilizes spatial multiplexing. By employing an off-axis interferometer with two orthogonally polarized reference beams at different angles, we multiplexed and recorded two polarization-sensitive interferograms using a single camera. Subsequently, the interferograms were demultiplexed in the Fourier domain. Through measurements of polarization-sensitive fields at various illumination angles, we successfully reconstructed 3D dielectric tensor tomograms. To demonstrate the effectiveness of our proposed method, we conducted reconstruction of 3D dielectric tensors for liquid-crystal (LC) particles with radial and bipolar orientational configurations.