Abstract: The polarographic behavior of rare earths with rhodamine Bin ammonium chloride solution has been further studied with Sm³⁺ as an another example. (1) In the presence of a small amount of diphenylguanidine, the addition of Sm³⁺ decreases the height of the adsorptive single-sweep derivative wave( -1.45V, SCE) as in the case of Y3 + does[1] There is a linear relationship between the concentration of 3×10^-7-2×10^-6M Sm³⁺ and the decreases of wave heights. (2) In the ammonium chloride solution with 10% dioxane, the complex of Sm³⁺ -rhodamine Bexhibits a reductive dc pola-rogram at -1.70V (SCE). The wave height is directly proportional to the concentration of Sm³⁺ within the range of 2×10^-6-2×10^-5M. Since the adsorptive wave of rhodamine Bprecedes the complex wave, it is hard to further increase the sensitivity either by dc or single-sweep polarography. Acomparison of RE-rhodamine Bcomplexes in dioxane was made in which Eu is more sensitive than Sm and Er is the most sensitive one among them.