Abstract: A reversible thermochromic material is disclosed in the application. The material is comprised of (A) an electron-donating chromatic organic compound and (B) an acidic phosphoric acid ester compound or metal salt thereof, wherein Components (A) and (B) are contained in a weight ratio of 1:1/10 to 50 by weight. The material may also contain a third Component (C) for controlling the temperature of coloration/decoloration of the thermochromatic material. The thermochromatic material undergoes reversible metachromatism at a temperature within the range of -50.degree. C. to 120.degree. C. Furthermore, the reversible thermochromic material may be contained within microcapsules.