This paper presents the FDTD thin-wire models of lossy wire structures with arbitrary inclination for transient analysis, which is difficult to address using traditional FDTD methods. The frequency-dependent losses of the conductors are fully taken into account, and the vector fitting technique is applied to deal with frequency-dependent parameters for time-domain analysis. The bidirectional coupling within the lossy coaxial conductors is modelled. The currents in inner and outer conductors are not necessarily balanced. Three cases are presented for the investigation of wave propagation velocity, wave attenuation, and current distribution. These data are compared with analytical results and numerical results using other models. It is found that the proposed thin-wire models can depict the transient behaviors in the lossy inclined conductors with the velocity error of less than 1%, and the attenuation error of less than 1.5%. Keywords -finite-difference time-domain (FDTD), thin-wire model, inclination, frequency-dependent loss I.