PURPOSE: To readily obtain the subject compounds useful as a herbicide in high yield by using a specific compound as a raw material.

CONSTITUTION: This method for producing 3,4-alkylene-1,3,4-thiadiazolidin-2-ones of formula II [R1 is H or a substituent group inert to the reaction; R2 is a halogen, nitro, methyl or methoxy; R3 is H or a halogen; (n) is 3-51, e.g. N-[5-(4- acetoxytetrahydrofuran-3-yloxycarbonylmethylthio)-4-chloro-2- fluorophenylaminothiocarbonyl]-N'-formylhydrazine is to react (A) 1,3,4- thiadiazolidin-2-ones of formula I with (B) a dihaloalkane of the formula X(CH2)nX (X is a halogen) in the presence of a base. Furthermore, the component (A) is preferably obtained by reacting thiosemicarbazides of formula IV prepared from isothiocyanates of formula III and formhydrazide with phosgene and hydrolyzing the resultant 3-formyl-1,3,4-thiadiazolidin-2-ones of formula V.