This paper presents an experimental study of using graphene oxide (GO) and modified GO to improve the interlaminar fracture and thermo-mechanical properties of glass fiber/epoxy composites. First, GO nanoplatelets were synthesized and then chemically modified using dodecylamin (DA-GO) and 1-(3-aminopropyl) imidazole (IL-GO) to improve their dispersion in the matrix and to reinforce epoxy adhesive. Each composite laminate was fabricated with six layers of glass fiber using the hand lay-up method and using 0.5wt% GO or functionalized GOs (FGOs) content. Dynamic mechanical thermal analysis was performed in three-point bending mode. The viscoelastic properties of all the composites have been further evaluated in the temperature range of 30-120 degrees C. The experimental results of double cantilever beam tests demonstrated that, with the addition of GO, DA-GO and IL-GO, the Mode-I force-displacement curves of the specimen increased by 7.5, 28.3 and 11.8%, respectively, compared to those of the control specimen. Like the GO, the DA-GO- and IL-GO-filled composites exhibited a rising R-curve, which was a sign of GO or FGO bridging and other toughening mechanisms such as crack pinning and bowing. It is remarkable to note that the maximum increase in Mode-I interlaminar fracture toughness and crack resistance were for the composite containing DA-GO nanoparticles. Dynamic mechanical analysis results showed that improvement in storage modulus and enhancement in the glass transition temperature of the composite have been achieved with the incorporation of only 0.5wt% of DA-GO into the GE composite. Thermo-gravimetric analysis showed that the degradation temperatures shifted to higher values after using GO and FGO nanoparticles.