PURPOSE: To industrially prepare the subject compound used as raw materials for production of herbicides or the like, profitably by reacting 3-(2-imidazolin-2- yl)picolinic acid with a metal hydroxide and subsequently with an acid in the presence of water while suppressing the formation of byproducts.

CONSTITUTION: A 3-(2-imidazolin-2-yl) picolinic acid of formula I is reacted with a metal hydroxide in the presence of water thereby forming 3-[(1- carbamoylpropyl)carbamoyl] picolinic acid of formula II. Further this product is reacted with an acid in the presence of water thereby obtaining the objective 2,3-pyridine-dicarboxylic acid shown by formula III which is useful for preparation of a herbicide of 2-(2-imidazolin-2-yl) nicotinic acid or the like. In formula I, X is H, methyl; Y, Z are each H, a halogen, a 1-6C alkoxy, a 1-4C alkylthio, a (substituted) phenyl or the like; R1 is a 1-4C alkyl; R2 is a 1-4C alkyl, a 3-6C cycloalkyl; R1 and R2 optionally form a methyl-substituted 3-6C cycloalkyl together with carbon atoms to which they bind.