The effects of membrane materials and the viscosity of the aqueous phase on the permeability of several kinds of polyamide microcapsules toward electrolytes were studied. The permeation rate of electrolytes was higher in the microcapsule membranes consisting of polyamide molecules with a polymethylene chain than in those having an aromatic ring. The viscosity of the microencapsulated aqueous phase decreased the permeation rate of electrolytes to a great extent, indicating that the diffusion of electrolytes in the interior of microcapsules is rate determining in the permeation process.