NEW MATERIAL:The compound of formulaI[R1 is alkyl, lower alkenyl, cyclopropyl, phenylcarbamoyl (the above groups may be substituted with lower alkyl, lower alkoxyl, or halogen), lower alkoxyl, lower alkylthio, phenyl, phenoxy, or halogen; R2 and R3 are H, lower alkyl or halogen; R1 and R2 may be bonded together at their terminals to form a heterocyclic group or cycloaliphatic group; when R1is Cl, CH3 or CF3, then at least one of R2 and R3 is lower alkyl or halogen].

EXAMPLE: 2-(m-Ethylphenyl)iminothiazolidine.

USE: Herbicide especially effective to Echinochloa oryzicola, Monochoria vaginalis, and other broad-leaved weeds grown in damp ground, and weeds in paddy rice field such as Eleocharis acicularis, Scirpus juncoides, Sagittaria pygmaea, etc., and giving little phytotoxicity to rice plant.

PROCESS: The compound of formula is prepared by cyclizing the compound of formula II (X is OH or halogen), if necessary in the presence of an acid.