PURPOSE: To prepare a herbicide composition containing a mixture of cyanazine and nitralin as an active component, exhibiting excellent synergistic effect especially to the weeds in plowed land compared with the separate use of each component, and having low phytotoxicity to crops.

CONSTITUTION: Cyanazine of formula I [2-(4-chloro-6-ethylamino-S-triazin-2-ylamino)-2-methyl-propionitrile] is mixed with nitralin of formula II [4-(methylsulfonyl)-2,2-dinitro-N,N-dipropylaniline] at a weight ratio of 4:1W1:4, and the mixture is used as an active component of a herbicide. Cyanazine is a known herbicide absorbable through the root and exhibiting herbicidal activity by inhibiting photosynthesis of the weeds, and having excellent herbicidal activity against broad-leaved weeds such as white-bird's-eye and gramineous weeds such as large crab-grass, and nitralin is a known herbicide absorbable through the root, having herbicidal activity by inhibiting the formation of cell wall in cell division, and exhibiting excellent herbicidal activity to the gramineous weeds such as barnyard grass, and umbrella sedge, etc.