Isothiocyanates and substituted pyrazoles were combined to form a series of novel isothiocyanates with highly effective herbicidal activity. The target compounds were analyzed by elemental analysis, 1H-NMR, EI-MS and IR spectroscopy. The synthesized compounds, particularly compounds 3-1 and 3-7, exhibited good herbicidal activities against four weeds. The EC(50) values of compound 3-1 against Echinochloa crusgalli L., Cyperus iria L., Dactylis glomerata L., and Trifolium repens L. were 64.32, 65.83, 62.42, and 67.72 µg/mL, respectively. The EC(50) values of compound 3-7 against E. crusgalli L., C. iria L., D. glomerata L., T. repens L. were 65.33, 64.90, 59.41 and 67.41 µg/mL, respectively. Compounds 3-1 and 3-7 may be further optimized as lead compounds for new herbicides.