Tensor impedance surfaces are modelled using a linear relationship between the tangential electric and magnetic fields at the surface, namely tensor impedance boundary condition (TIBC). To implement TIBC in the finite-difference time-domain (FDTD) method, a problem arises: TIBC boundary condition requires that the tangential components of the electric and magnetic fields to be co-located in both spatial and time grids. However, this requirement is not compatible with the classical leapfrog Yee's algorithm. In this study, the authors present an algorithm for FDTD implementation of TIBC. Numerical examples are presented to demonstrate the stability, and the accuracy of the proposed approach. Validation is achieved by comparison with analytic solutions.