Fibrous nanofluidic materials are ideal building blocks for implantable electrode, biomimetic actuator, and wearable electronics due to their favorable features of intrinsic flexibility and unidirectional ion transport. However, the large-scale preparation of fibrous nanofluidic materials with desirable mechanical strength and good environment adaptability for practical use remains challenging. Herein, by fully taking advantage of the attractive mechanical, structural, and chemical features of boron nitride (BN) nanosheet and nanofibrillated cellulose (NFC), a scalable and cost-effective three-dimensional (3D) printed macrofiber featuring abundant vertically aligned nanofluidic channels is demonstrated to exhibit a good combination of high tensile strength of 100 MPa, thermal stability of up to 230 °C, and ionic conductivity of 1.8 × 10⁻⁴ S/cm at low salt concentrations (< 10⁻³ M). In addition, the versatile surface chemistry of cellulose allows us to stabilize the macrofiber at the molecular level via a facile post-cross-linking method, which eventually enables the stable operation of the modified macrofiber in various extreme environments such as strong acidic, strong alkaline, and high temperature. We believe this work implies a promising guideline for designing and manufacturing fibrous nanodevices towards extreme environment operations.