To evaluate the effects of water quality and adjuvant (ammonium sulfate) in glyphosate herbicide efficiency, a factorial experiment based on RCBD with three replications was conducted at Research Garden of Faculty of Agriculture, University of Birjand in 2010-2011. Experimental factors were different water quality in three levels of medium hard water with 2950 ppm, hard water with 4774 ppm total soluble concentration, and listilled water (soft water) glyphosate (roundup) dose in four levels including 2, 4, 6 and 8 lit.ha-1 and using and not using the adjuvant (ammonium sulfate at 6 kg.ha-1). The results showed that raising herbicide dose increased the reduction density percentage of broad and narrow leafweeds. Application of soft water with herbicide had the most reduction density percent and showed significant differences with other waters, so that the most and the lowest reduction density percentages with average 93 and 10.88 percent belonged to soft water with glyphosate dose of 8 lit. ha-1 and hard water with glyphosate dose of 2 lit.ha-1,respectively. But this application between doses of 6 and 8 lit. ha-1 with soft water was nonsignificant. Also, results showed that application of ammonium sulfate with hard water on reduction density percentage was nonsignificant, but had more effect on broad leaves species compar with narrow leaves. Totally, the effect of different factors on reduction density percentage increased over time. Generally with regard to economic and environmental factors, spraying 6 lit.ha-1of glyphosate with high quality water can be recommended for adequate control of barberry garden weeds.