This study aims at investigating the relationship between the ratio of dispersion coefficient to molecular diffusion coefficient (DL/Dm) and Peclet number (Pe) for a multi-solute system in non-Darcian flow regimes. Existing understanding on solute dispersion is primarily derived from Darcian flow regime with one solute. We find that solute dispersion in rock fractures can be characterized by the mechanism of both macrodispersion and Taylor dispersion, in non-Darcian flow domains. For the Darcian flow regime, different solutes lead to the same DL/Dm-Pe relationship. However, as the flow becomes non-Darcian, solute with a higher molecular diffusion coefficient result in higher DL/Dm at the same Pe than that with a lower diffusion coefficient. ¿ 2001 American Geophysical Union