<p>This research aims to investigate the effect of sub-zero temperature on the interlaminar fracture toughness of glass fiber reinforced polymer with multiwalled carbon nanotube filler. was used to test panels were fabricated using hand layup technique followed by placing it under uniform pressure. Test samples were soaked in dry Ice for several minutes before testing. Samples for modes I and II interlaminar fracture toughness were prepared and tested according to ASTM D5528, and D7905, consequently. The results showed that the room temperature mode I interlaminar fracture toughness GIc improved by 18.54 % when 0.15 % (weight% of the resin) carbon nanotubes (CNT) was added to the resin and improved by 42.06 % when tested at sub-zero temperature using dry ice box. Mode II interlaminar fracture toughness, GIIc improved by 48.17 % when 0.15 % (weight% of the resin) carbon nanotubes (CNT) was added to the resin and improved by 54.64 % when tested at sub-zero temperature using dry ice box. Ultimate tensile strength decreased by 8 % when CNT was added to the matrix at room temperature, however, when tested at sub-zero temperature the ultimate tensile strength decreased by 4.82 % for plain GFRP and decreased by 11.81 % for hybrid GFRP. Modulus of elasticity decreased when adding 0.15 %wt CNT by 4.14 % at room temperature and decreased again when tested at sub-zero temperature by 0.57 % for plain GFRP and decreased by 6.28 % for hybrid GFRP, respectively. SEM images of mode 1 and mode II specimens fracture surfaces showed that GFRP samples with added CNT matrices have a rougher surface at RT than that of plain samples. The results for GIc and GIIc of samples are consistent with the observation of the fracture surface.</p>