Abstract: The sample was melted with sodium hydroxide at 650 ℃ and treated with hydrochloric acid.Then the silicon was separated by gravimetric method using animal glue for fast agglomerating silicon acid and the iron in the sample determined by spectrophotometry with sulfosalicylia acid.The result indicated that the iron content of 0.714 μg/L could be accounted with the Lambert-Beer law.A=0.013+1.29C,ε=5.3×104 L·mol-1·cm-1;r=0.999 5.The method had been applied to the determination of iron in perlite with the relative standard deviation of 0.51%～0.75% and the results obtained were accurate.