PURPOSE: To obtain a 2,4,6-triiodoisophthalic acid amide by using an α- hydroxypropionyloxyamino-substituted-2,4,6-triiodoisophthalic acid amide protected with acyl at 5-site as a raw material, hydrolyzing the amide compound with an alkaline earth metal hydroxide and removing the residual metal as a water-insoluble precipitate.

CONSTITUTION: A compound of formula I (X is acyl; Y is H or acyloxy; C3H5(OH)2 is 1,3-dihydroxyisopropyl or 2,3-dihydroxypropyl) is hydrolyzed with an alkaline earth metal hydroxide. An acid is added to the reaction mixture after the reaction to precipitate the residual alkaline earth metal in the form of a water-insoluble precipitate and the precipitate is removed by filtration, etc., to obtain the objective 2,4,6-triiodo-isophthalic acid amide of formula II (R is H or OH) in high purity. The compound of formula II is useful as a contrasting component of an X-ray contrasting agent and the absence of alkaline earth metal salt is advantageous for the above purpose.