This paper investigates the effect of fiber concentration on the mechanical and thermal characteristics of the (3-Aminopropyl) triethoxysilane treated basalt fiber (BF) reinforced acrylonitrile-butadiene-styrene (ABS) composites. The composites are produced with extrusion process and get final shape with injection moulding process. The ratio of the BF used in the composites is 5, 10, 20 and 30 wt%. The characterization of the composites is performed via tensile, flexural, impact tests, dynamic mechanical analysis (DMA) and thermal gravimetric analysis (TGA). Correlation analyses are also performed to determine the relationships between the tensile, flexural and impact properties. When the test results are considered, a remarkable improvement in the tensile strength is achieved in high BF (20 and 30 wt%) containing composites. As the concentration of BF increases, the flexural strength improves steadily. The elastic modulus shows a rising trend as the BF ratio increases. The addition of BF causes increase at 4 degrees C in glass transition temperature (T-g). From TGA analysis, the main decomposition step of ABS is not change and the residue yield increases as the added amount of BF increases. An excellent directly linear correlation is determined between the tensile and flexural strength, while the impact strength shows a good inversely linear correlation with the tensile and flexural strength.