AbstractAn enormously low loss symmetrical hybrid decagonal porous core spiral photonic crystal fiber (SH-PCF) has been proposed for terahertz (THz) wave guiding. The modal characteristics of the fiber and its mathematical analysis have been numerically completed using a full-vector finite element method (FEM). Simulation results show an ultra-low material loss of 0.0167 cm⁻¹ and large effective area 1.95×10⁶ µm² which is 91.6 % of bulk absorption material loss at controlling frequency f=1.0 THz with a core porosity 42 %. Additionally, proposed structure establishes the comparatively higher core power fraction maintaining lower scattering loss about 1.8×10⁻¹⁵ dB/cm at the same operating frequency. It promises the aforementioned advantages for efficient THz wave propagation.