Cesium iodide is a colorless crystalline or crystalline powder with the chemical formula CsI. Easy to decompose and sensitive to light. Extremely soluble in water, soluble in ethanol, slightly soluble in methanol, almost insoluble in acetone. Relative density 4.5. Melting point 621 ℃. The boiling point is about 1280 ℃. The refractive index is 1.7876. It is stimulating. Toxic, with a median lethal dose (rat, intraperitoneal) of 1400mg/kg and (rat, oral) of 2386mg/kg.