The fractal geometry is a non-Euclidean geometry which describes the naturally irregular or fragmented shapes, so that it can be applied to fracture surface of a material to investigate the fracture process. The fractal dimension of irregular surface has fractal values ranging from 2 to 3, and that of irregular line profile has fractal values ranging from 1 to 2. In this investigation, this fractal geometry was appiled to the fracture surface of Al-Li alloy in order to correlate the fracture phenomena to microstructures of this alloy. Vertical section fracture profile methods were used to determine the fractal dimension, D_F. We found a correlation between fractal dimension and toughness of the alloy. More specifically, the logarithm values of toughness increased with those of (D_F-1), but not linearly when arbitrary lengths of measuring unit were used to depict the fracture line profile. However, a very good linear correlation was observed when the length of measuring unit was chosen such that its magnitude is of microstructural size. The microstructures affecting fracture processes were found to be grain size, slip step and fibering size in Al-Li alloy.