<p>In order to solve the problems of strong hygroscopicity and poor dimensional stability of bio-based nylon 56, physical and chemical modification methods can be used to modify bio-based nylon 56 composites. In this paper, basalt fiber (BF) reinforced bio-based nylon 56 composites with different contents were prepared by melt blending method, and their structure, mechanical properties and thermal properties were characterized. Studies show that bio-based nylon 56/BF composite materials were less dense than 1.540&#xa0;g/cm³, Studies showed that the density of the bio-based nylon 56/BF composites was less than 1.540&#xa0;g/cm³, BF was tightly wrapped by bio-based nylon 56 matrix resin, and the interfacial bonding between them was strong. Compared with pure bio-based nylon 56, the mechanical properties of bio-based nylon 56/BF composites were significantly improved by the addition of BF. When BF was added by 50%, the bending strength was 214.4&#xa0;MPa, the flexural modulus was 10,117&#xa0;MPa, which increased by 138.67% and 345.16%, respectively. The impact strength was 12.5&#xa0;kJ/m², which increased by 316.6%, the water absorption was 0.84%, which decreased by 75%, and the shrinkage was 0.01%, which decreased by 98.01%. As the increase of basalt fiber content, the relative crystallinity of the composites can reach 9.03%, and the thermal decomposition temperature increases slightly. The bio-based nylon 56/BF composite materials have low density and excellent mechanical properties, and BF gives bio-based nylon 56 resins a high added value for a wide range of applications such as automobile engine covers and wind turbine blades.</p> Graphical Abstract <p></p>