Abstract An attempt has been made to apply gel filtration on Sephadex to micellar solutions of surfactants. The data on the gel filtration of surfactants were interpreted by taking into account the fact that there exist both micellized and unmicellized species in the solutions. A simple method for obtaining the retention volume of the micelle (VM) of a surfactant directly from the elution curve was developed. Further, the relation between the values of VM and the micellar molecular weights (MMW) was examined for various types of surfactants. A linear relation was found between VM and log MMW, with the exception of a surfactant with a heterocyclic structure. It appears that gel filtration offers a convenient way for roughly estimating the MMW’s of surfactants.