The movement of K, Ca, Fe, Br and Rb in the urine of Rb-treated rats is investigated by means of PIXE (particle induced X-ray emission) measurements. The excreted amount of Rb per day in urine becomes maximum 1 or 2 days after intraperitoneal injection and then exponentially decreases with a biological half time of 6.60 ± 1.58 days. The integrated amount of excreted Rb in urine over 14 days was 40-50% of the injected one, which is nearly one order of magnitude larger than the previous result obtained by the measurement on Rb-ingested rats. No outstanding time dependencies of the excretion amount per day are found for other elements. Relations between the excretion amounts per day for Rb and those for other elements are less evident.