Abstarct: Spiders are one of the most abundant groups of arthropods on earth, with about 49,000 species in 131 families in the world and 906 species in 55 families identified in Iran. Although many studies have been done on Iranian spider fauna, many parts of the country have not yet been studied. Spiders are an important component of the terrestrial ecosystem and play a key role in controlling insect populations. Spiders are also important as part of biodiversity with positive functions such as pest hunting, in the sustainability of agricultural production systems and natural areas. The aim of this study was to identify the fauna and study the biodiversity of spiders in Shahroud. Spiders were sampled from different habitats such as agricultural lands, pastures, gardens and urban green space of the city during 2018-19. To study the biodiversity of spiders in three ecosystems of garden, pasture and wheat field, spiders were collected every two weeks by pit trap and survey collection methods. Samples were stored in 80% ethanol and examined by stereomicroscope. In this study 23 species belonging to 21 genera from 18 families were identified. Five families and eleven species are reported for the first time from Semnan provinc. The values of biodiversity indices calculated for the three studied ecosystems, for Simpson index 0.67, 0.78 and 0.69, for Shannon-Weiner index 1.09, 1.33 and 1.03 and for Margalf index 1.19 , 1.53 and 1.17 were calculated, which indicates the more appropriate status of biodiversity indices of garden ecosystems than the other two ecosystems. The species identified in this study are: Agelescape gideoni, Clubiona neglecta, Uloborus walckenaerius, Dysdera crocata, Anagraphis pallens, Castianeira arnoldii, Xysticus cristatus, Tetragnatha extensa, Pholcus phalangioides, Pisaura mirabilis, Cyrba ocellata, Philaeus chrysops, Plexippoides flavescens, Oecobius ferdowsii, Oecobius Sp, Thanatus atratus, Steatoda ephippiata, Pardosa hortensis, Pardosa italic, Trochosa hispanica, Oxypoes Sp, Neoscona adianta, Frontinellina frutetorum.