Na⁺ balance was studied in Rana temporaria, which hibenates in fresh water in the winter time. Na⁺ uptake rate, skin Na⁺ loss rate, urinary Na⁺ loss rate and Na⁺-K⁺ adenosine triphosphatase(ATPase) were measured at two different temperatures 1 ~ 2℃ and 20 ~ 24℃ respectively. The results obtained were as follows: 1. Na⁺ uptake rates in the frog in an artificial Pond water (APW) were found to be 8.28±0.73 and 2.19±0.37 μEq/g/day at 20 ~ 24℃ and 1.0 ~ 2.5˚ respectively. 2. Na⁺ loss rate through the frog skin to APW were found to be 4.26±0.72 and 0.93±0.21 μEq/g/day at the same temperatures. 3. Mean rates of urinary Na⁺ loss at 20 ~ 24℃ and 3 ~ 4℃ were found to be 3.02±0.73 and 0.78±0.13 μEq/g/day respectively. 4. The activities of Na⁺-K⁺ activated ATPase of frog skin fragments were found to be 258±39.4 and 49.6±7.1 μM Pi/g protein/hr at 24℃ and 2℃ respectively. From the above results, it may be concluded that frogs can take up enough Na⁺ through the skin from APW exceeding skin loss Plus urinary loss at 1 ~ 2℃. It is suggested that Na⁺ transport across frog skin is closely related with Na⁺-K⁺ ATPase since Q₁₀ of Na⁺ uptake is much similar to that of the activities of Na⁺-K⁺ ATPase.