Purpose Fused filament fabrication of continuous-fiber-reinforced polymers is a promising technique to achieve customized high-performance composites. However, the off-axis tensile strength (TS) and Mode I fracture toughness of fused filament fabricated (FFFed) continuous-glass-fiber-reinforced (CGFR) nylon are unknown. The purpose of this paper is to investigate the mechanical and fracture behavior of FFFed CGFR nylon with various fiber content and off-axis fiber alignment. Design/methodology/approach Tensile tests were performed on FFFed CGFR-nylon with 9.5, 18.9 and 28.4 fiber vol. %. TS was tested with fiber orientations between 0∘ and 90∘ at 15∘ intervals. Double cantilever beam tests were performed to reveal the Mode I fracture toughness of FFFed composites. Findings TS increased with increasing fiber vol. % from 122 MPa at 9.5 vol. % to 291 MPa at 28 vol. %. FFFed nylon with a triangular infill resulted in 37 vol. % porosity and a TS of 12 MPa. Composite samples had 11–12 vol. % porosity. TS decreased by 78% from 291 MPa to 64 MPa for a change in fiber angle θ from 0∘ (parallel to the tensile stress) to 15∘. TS was between 27 and 17 MPa for 300 < θ < 900. Mode I fracture toughness of all the composites were lower than ∼332 J/m2. Practical implications Practical applications of FFFed continuous-fiber-reinforced (CFR) nylon should be limited to designs where tensile stresses align within 15∘ of the fiber orientation. Interlayer fracture toughness of FFFed CFR composites should be confirmed for product designs that operate under Mode I loading. Originality/value To the best of the authors’ knowledge, this is the first study showing the effects of fiber orientation on the mechanical behavior and effects of the fiber content on the Mode I fracture toughness of FFFed CGFR nylon.