IN ORDER TO STUDY RESPONSES OF BARNYARDGRASS [ECHINOCHLOA CRUS-GALII (L.) P. BEAUV.] AND VELVETLEAF (ABOTILON THEOPHRASTI MEDICUS.) TO GLYPHOSATE AND NICOSULFURON AT 0, 0.125, 0.25, 0.5, 1, 2 AND 3 L/HA DOSAGES, AN EXPERIMENT WAS DONE IN 2008-9 AT RESEARCH GREENHOUSE OF THE FERDOWSI UNIVERSITY OF MASHHAD. EXPERIMENTS CONDUCTED AS FACTORIAL ARRANGEMENT OF TREATMENTS BASED ON RANDOMIZED COMPLETELY DESIGN WITH SIX REPLICATIONS AND TWO TIMES. RESULTS SHOWED SIGNIFICANT EFFECT OF HERBICIDE DOSAGES ON SURVIVAL PERCENTAGE, VISUAL ASSESSMENT (BASED ON EWRC), PLANT HEIGHT, PLANT HEIGHT (SPAD READING) AND LEAF AREA OF WEEDS (P£0.01). DOSE RESPONSE CURVES OF BARNYARDGRASS BIOMASS (TO COMPARE WITH CONTROL) AT TWO HERBICIDES WERE SIMILAR, BUT VELVETLEAF BIOMASS SHOWED DIFFERENT RESPONSES TO HERBICIDES. SO THAT, TO REDUCTION 50 PERCENT OF VELVETLEAF BIOMASS ABOUT 1.7 FOLD NICOSULFURON WAS NEEDED TO COMPARE WITH GLYPHOSATE. IN GENERAL, BECAUSE OF ACTIVE INGREDIENT OF NICOSULFURON IS LOWER THAN GLYPHOSATE IN FORMULATION AND IT SELECTIVE PROPERTY, WAS RECOMMENDS TO CONTROL OF BARNYARDGRASS AND VELVETLEAF WEEDS IN CORN.