To study weed species diversity and COMMUNITY structure in pistachio (Pistacia vera L.) orchards in 33 orchards of 12 villages an investigation was conducted in Bardaskan County, Khorasan Razavi Province, Iran during 2008-2009. weed population sampling was conducted in a w shape method using 1m² quadrate. the results showed that the WEEDS of pistachio orchards were belonging to 15 families and 44 species.dicotyledons (31 species) were more than monocotyledons (13 species). Such as in this COMMUNITY, weed species of C3, C4, annual and perennial were 26, 18, 28 and 13, respectively. the majority of weed species were belonging to the plant families of chenopodiceae (9 species) and poaceae (12 species) amongst dicotyledons and monocotyledons, respectively. the most important species of monocotyledon annual WEEDS were including Echinochloa crus-gali, Digitaria sanguinlis, Setaria viridis and perennial WEEDS were including Cyperus routundus, Cynodon dactylon and convolvulus arvensis. weed species were grouped in seven clusters for density average, frequency and uniformity (similarity 75 percent) whereas in eight clusters for relative density average, relative frequency and relative uniformity (similarity 75 percent). amplitude changes of Shannon-winter diversity index were between 2.3 and 0.16 and of Simpson dominant index were between 0.97 and 0.17. the difference among indices of biodiversity and dominant clusters were relative to scale and type of management practices.