Pore-structure is one of important factors affecting the properties of porous metal materials, but it is difficult to describe the complexity of pore-structure exactly. Fractal theory is a very effective method for investigating pore-structure of porous metal materials, which builds a bridge between micro-morphology and macroperformance. In the paper, two kinds of stainless steel powder for different powder images (irregular and spherical shapes) with particle size of 38 mu m-150 mu m were used to prepare samples to a preset porosity, which ranged from 20.4% to 45.5%, by conventional compaction technique, and then sintered at 1250 degrees C for 2 h in the vacuum. The porosity and microstructure of sintered samples were analyzed using the Archimedes' law and the optical microscope, respectively. In addition, the pore-structure was studied by fractal theory and the fractal dimension was calculated using the box counting method. The results show that the fractal dimension decreases continuously with the increase of magnification, from 1.43 to 1.25 for irregular powder, and the optimal magnification ranges from x 200 to x 500, but it increases gradually with the increase of porosity. Furthermore, the relationships between the fractal dimension and the magnification or porosity can be expressed by the model of D = a(0) exp(-x/a(1)) + a(2) or D = k(2) - k(1)-k(2)/a + exp(a-k(0)/k(3)) respectively. Crown Copyright (C) 2011 Published by Elsevier By. All rights reserved.