Nitrogen (N)-doped diamond (N-D) is one of the most important carbon-based electronic materials and has many interesting and unique features in terms of physics owing to the presence of N related color centers. In this paper, the terahertz (THz) magneto-optical (MO) properties of N-D grown by microwave plasma chemical vapor deposition (MPCVD) are investigated. By using polarized THz time-domain spectroscopy (TDS) in the presence of magnetic field from 0 to 8 T, the THz transmission through an N-D sample in Faraday geometry is measured at 80 K. The dependence of the Faraday rotation angle and ellipticity, the complex transverse or Hall MO conductivity and the complex dielectric constant upon the magnetic field for N-D are examined. The results show that N-D has excellent THz MO Faraday rotation effect and can be applied as THz rotatory material.