This study investigates the use of magnesium hydroxide (Mg(OH)₂) nanoparticles as a versatile nanofiller in polylactic acid (PLA) composite bone scaffolds fabricated via fused deposition modeling (FDM) 3D printing. The addition of Mg(OH)₂ improved the mechanical properties of PLA scaffolds, with a 5 wt% addition increasing tensile and compressive strengths by 20.50% and 63.97%, respectively. The alkaline degradation products of Mg(OH)₂ neutralized the acidic degradation products of PLA, accelerating its degradation. The PLA/20Mg(OH)₂ scaffold showed a significantly higher weight loss rate (15.40%) compared to pure PLA (0.15%) after 28 days. The composite scaffolds released Mg²⁺ over 28 days, promoting biomineralization and apatite deposition. Bone marrow mesenchymal stem cells (BMSCs) showed enhanced adhesion, proliferation, and osteogenic differentiation on scaffolds with 5 wt% Mg(OH)₂, attributed to Mg²⁺ release. The study highlights that Mg(OH)₂ can address issues related to degradation, mechanical properties, and cell interaction in polymer scaffolds, offering promising applications in tissue engineering. The optimal Mg(OH)₂ content for mechanical and degradation performance was found to be 5 wt%, while 20 wt% provided the best degradation and biomineralization. The results suggest that Mg(OH)₂ is a promising additive for improving the performance of PLA-based bone scaffolds.This study investigates the use of magnesium hydroxide (Mg(OH)₂) nanoparticles as a versatile nanofiller in polylactic acid (PLA) composite bone scaffolds fabricated via fused deposition modeling (FDM) 3D printing. The addition of Mg(OH)₂ improved the mechanical properties of PLA scaffolds, with a 5 wt% addition increasing tensile and compressive strengths by 20.50% and 63.97%, respectively. The alkaline degradation products of Mg(OH)₂ neutralized the acidic degradation products of PLA, accelerating its degradation. The PLA/20Mg(OH)₂ scaffold showed a significantly higher weight loss rate (15.40%) compared to pure PLA (0.15%) after 28 days. The composite scaffolds released Mg²⁺ over 28 days, promoting biomineralization and apatite deposition. Bone marrow mesenchymal stem cells (BMSCs) showed enhanced adhesion, proliferation, and osteogenic differentiation on scaffolds with 5 wt% Mg(OH)₂, attributed to Mg²⁺ release. The study highlights that Mg(OH)₂ can address issues related to degradation, mechanical properties, and cell interaction in polymer scaffolds, offering promising applications in tissue engineering. The optimal Mg(OH)₂ content for mechanical and degradation performance was found to be 5 wt%, while 20 wt% provided the best degradation and biomineralization. The results suggest that Mg(OH)₂ is a promising additive for improving the performance of PLA-based bone scaffolds.