AbstractUsing the Moon’s natural resources to build infrastructure is the first step toward lunar colonization. Lunar regolith, rich in aluminosilicate, has the potential to prepare geopolymer for construction. In this paper, carbon nanofibers (CNFs) were added to geopolymers based on lunar regolith simulant, aiming at reinforcing mechanical and microstructural properties. A ball-milling method of CNF dispersion into the lunar regolith simulant was evaluated. The mechanical properties of the resulting geopolymer nanocomposites was investigated. X-ray diffractometry, scanning electron microscopy, Fourier transform infrared spectrometry, and mercury intrusion porosimetry were used to characterize the microstructural properties. The results indicated that the mechanical properties were improved by CNFs and that the optimal content was 0.3% by weight. Also, flexural strength, Young’s modulus, flexural toughness, peak displacement, and compressive strength were reinforced by 34.8%, 7.5%, 83.9%, 21.4%, and 13.1%, respectively. Microstructural results suggested that the CNFs acted as nucleation, fillers, and bridges in the nanocomposites, leading to lower porosity, higher energy requirement for failure, and higher mechanical properties, which are considerable for lunar-based construction.