It is well known that subsurface contaminant transport is significantly influenced by heterogeneous distributions of the relevant hydraulic properties. A practical scheme to deal with these heterogeneous distributions may be the combination of the two commonly used approaches, the so-called equivalent homogeneous and heterogeneous approaches. As an important step to establish such a hybrid approach, this brief communication is devoted to determining block scale dispersivity in porous media characterized by Gaussian stochastic fractals. Sensitivity analyses indicate that block scale dispersivity is a strong function of block size and anisotropy in K.¿ 1997 American Geophysical Union