The herbicidal activity of thiocarbamate herbicides and its effect on cell division and elongation were determined. The herbicides studied were molinate(S-ethyl-N,N-hexamethylenethiocarbamate), dimepiperate [S-(${alpha}$,${alpha}$-di methylbenzyle)piperidine-1-carbothioate], esprocarb [S-benzyl-N-ethyl-N-(1,2-dimethylpropyl) thiocarbamate], and thiobencarb [S-(4-chlorobenzyl)-N, N-diethylthiocarbamate]. The herbicides applied at the rates ranged from $10^{-6}$ to $10^{-5}M$ did not affect germination and post-germination root growth of rice(Oryza sativa L.) and barnyardgrass [Echinochloa crus-galli(L.) P. Beauv.], but inhibited the post-germination shoot growth. There was no inhibition of gibberellin-induced ${alpha}$-amylase biosynthesis in de-embryonated rice seeds by the herbicides at $10^{-5}M$, but about 50-60% inhibition occurred at $10^{-4}M$. When the herbicides were applied 7 days after seeding, the rates required to 50% growth inhibition of barnyardgrass were 146g, 91g, 96g, and 102g ai/10a for molinate, dimepiperate, esprocarb, and thiobencarb, respectively. No effect of the herbicides on cell division was found at $10^{-4}M$, but about 31 to 47% inhibition as compared with the untreated check was obtained by treatment of the herbicides at $10^{-3}M$. However, about 33 to 38% inhibition of cell elongation occurred at $10^{-5}M$ of the herbicides. They also inhibited IAA-induced cell elongation.