PURPOSE: To obtain a 2-fluoroisobutyric acid ester useful as an intermediate for a triazine-type herbicide from a methacrylic acid ester with single reaction step in high yield at a low cost.

CONSTITUTION: The objective 2-fluoroisobutyric acid ester is produced on an industrial scale at a low cost by reacting a methacrylic acid ester, e.g. a compound of formula I (R is alkyl, aryl, aralkyl or alkoxyalkyl) with (a) preferably an essentially anhydrous hydrogen fluoride source such as hydrogen fluoride and (b) an amine such as aromatic amine (e.g. pyridine, melamine or collidine) or tertiary aliphatic amine (e.g. trimethylamine or tributylamine) at a weight ratio (a/b) of usually 50/50 to 99/1, preferably 70/30 to 95/5 in the presence of preferably a Lewis acid catalyst preferably at 20-150°C especially 50-120°C. The compound is useful as an intermediate for the compound of formula II having excellent herbicidal effect, etc., and free from phytotoxicity to paddy rice plant.