(90)Y is a high-energy radioisotope and emite β-ray with 2.6 days half life. (90)YCl(3) colloid has been used for malignant tumor therapeutically, as (198)Au colloid. In the present experiment, the purification of (90)Y, and the detection of the contaminated (90)Sr was studied. Amberlite XE-100 column was suitable for this prupose. The colloidal size of (90)YCl(3) was transformed by pH, and the features of (90)YCl(3) colloids were observed on electrone microscope. 1) (90)Y and (90)Sr mixture adsorbed on Amberlite XE-100 column (100-200 mesh, 2.5 column volume), and eluted by 0.5 N HCl. (90)Sr is eluted out at 10-60 ml, and (90)Y is eluted out from 170 ml. 2) A mixture of 20 mC of citrate-(90)Y complex and 1μC of (90)Sr fixed on this column, and then eluted by 0.5 N HCl. One drop of eluate at 10 ml was detectable by GM counter. The detectable lower limit of contaminated (90)Sr is 0.1μC by re-counting on GM counter 24 hrs after the elution. 3) Amberlite XE-100 column is suitable for the second column on the milking system, for the purpose of separating the contaminated (90)Sr and (90)Y. This procedure is complete in 1 hr process. 4) (90)YCl(3) colloid is aggregated and formed clamp in high pH solution, Electrone microscopic observations showed that the colloidal size was 40-50 mμ at pH 5, and 20 mμ at pH7.