PURPOSE: To simply produce aminooxyacetic acid which is useful as a plant protective agent and a useful intermediate substance for producing agricultural chemicals and medicines and its acid addition salt in high yield.

CONSTITUTION: An oxime expressed by formula I (R is methyl or ethyl) is reacted with chloroacetic acid in the presence of solid potassium hydroxide in dioxane at 80°C for 2hr to provide an 0-substituted oxime expressed by formula II. The resultant compound is then hydrolyzed with dilute hydrochloric acid to afford hemihydrochloride of aminooxyacetic acid expressed by formula III.