(1) The color reaction between iodine and basic acetate is not, as is often believed, peculiar to lanthanum. It is shown also by praseodymium, neodymium and samarium. (2) The absorption maximum of iodine-basic acetate shifts to shorter wave-length side with the decrease of the basicity of the rare earth elements. (3) The color change of iodine-basic acetate with the lapse of time was studied photometrically. (4) It was confirmed that the sorption isotherm holds good in the cases of the basic acetates of lanthanum, praseodymium and neodymium. (5) The effect of other ions on the color reaction was discussed.