The magnesium hydroxide (MH) whiskers / ABS composites were prepared by melt-extrusion with modified whiskers as filler. The mechanical performances, including the tensile strength, elongation at break and elastic modulus, were tested by electronic universal testing machine. The results showed that with the increasing of the whisker dosage, the tensile strength and elongation at break reduced gradually, and the elastic modulus get maximum when it is 25%.The morphology on fracture of composites was analyzed by SEM. The conclusions are the whiskers of surface modifications can be evenly distributed in the composites and bond partly with ABS. that it is necessary to enhance the combine strength of interface on excellence performances of composites.