The effects of extrusion ratio and extrusion temperature on tensile strengths and microstructures of 20 vol.% SiCw-2124A1 composites were investigated. The alignment of SiC whiskers along the extrusion direction in SiCw-2124A1 composites was improved and the aspect ratio of SiC whiskers was decreased with increasing extrusion ratio from 10:1 to 25:1. The SiCw-2124A1 composite exhibited the highest tensile strength at the extrusion ratio of 15:1. The aspect ratio of whiskers and the relative density of composite increased with increasing extrusion temperature from 470 degrees C to 530 degrees C. The tensile strength of SiCw-2124A1 composite increased with increasing extrusion temperature up to 530 degrees C. Based on the concept of the load transfer efficiency of misoriented SiC whiskers in the 2124A1 matrix, the two microstructural parameters of the alignment and aspect ratio of whiskers, which influenced on the tensile strength in an opposite way, were combined into a single parameter proposed as an effective aspect ratio. The highest tensile strength of SiCw-2124A1 composite at the extrusion ratio of 15:1 is explained by the largest effective aspect ratio due to the balance of the alignment and aspect ratio of SIC whiskers. A modified phenomenological equation describing the tensile strength of SiCw-2124A1 composites as a function of microstructural parameters was proposed by introducing the effective aspect ratio as a substitute for the average aspect ratio of SIC whiskers.