The NASA Artemis program is propelling progress in space settlement and exploration. In-space manufacturing (ISM) plays a crucial role in extended space explorations, and additive manufacturing (AM) holds significant promise. Polyether ether ketone (PEEK) is an excellent material for Lunar environments and can be 3D printed using fused filament fabrication (FFF), which offers advantageous versatility over other techniques. Incorporating Lunar regolith into PEEK can reduce ISM costs. This study focuses on the FFF of PEEK/regolith composites and compares them with pure PEEK and PEEK/carbon fiber. Higher solid material content presents challenges during extrusion, leading to increased sample porosity. The addition of 20 wt% carbon fiber enhances tensile strength by 8.37%, whereas introducing 15 and 30 wt% Lunar regolith reduces tensile strength by 14.63% and 26.78%, respectively, resulting in more brittle fractures and reduced elongation at break. These findings hold significant implications for advancing AM in Lunar environments and ISM.