In the automotive industry, porous aluminum is expected to be used as a new functional material because of its light weight, high energy absorption and high sound-insulating property. Recently, a new processing route for fabricating the porous aluminum precursor, which utilizes friction stir processing (FSP), has been developed. It is expected that, by applying the FSP route precursor method, the cost-effective fabrication of porous aluminum with high productivity can be realized. In this study, two different types of A1050 porous aluminum were fabricated from two different sizes of precursor by the FSP route precursor method. The two types of porous aluminum fabricated using small and large precursors are hereafter referred to “FSP-S porous aluminum” and “FSP-L porous aluminum”, respectively. The pore structures of FSP-S porous aluminum, FSP-L porous aluminum and also commercially available porous aluminum (ALPORAS, fabricated by Shinko Wire Co., Ltd.) were nondestructively observed by X-ray computed tomography (X-ray CT). From the nondestructive observation of pore structures, it was shown that a large number of pores of smaller area and volume were distributed in porous aluminum fabricated by the FSP route precursor method compared with the pores in ALPORAS. However, there was little difference in the circularity of pores between porous aluminum fabricated by the FSP route and ALPORAS, and there was little dependence of the pore structure on the precursor size for porous aluminum fabricated by the FSP route. This result indicates the potential of the FSP route for fabricating larger porous aluminum samples.