The effects of kanendomycin on the potassium permeability in the rabbit erythrocyte membrane are investigated and the results are summarized as follows. 1. Kanendomycin causes the efflux of K⁺ and influx of Na⁺ across the rabbit erythrocyte membrane. 2. Osmotic resistance of kanendomycin treated erythrocytes is diminished. This diminution of osmotic resistance is more pronounced by increasing concentration of kanendomycin and longer incubation time. But osmotic resistance is rather increased in the presence of lower concentration of kanendomycin. 3. Cysteine and glutathione have little influence on K⁺ efflux induced by kanendomycin. 4. EDTA has no effect on the increase in K⁺ outflux by kanendomycin while PCMB augments slightly on K⁺ outflux. 5. Kanendomycin inhibits Ca⁺⁺ binding competitively to rabbit erythrocyte membrane fragments.