In order to study the biodiversity of plant parasitic nematodes of citrus orchards in Dezful and Andimeshk, in northes of Khuzestan province, 115 soil and root samples were collected from rhizosphere of citrual trees in spring, autumn and summer in 2016 and 2017 years. Nematodes were extracted by centrifugal flotation technique and transferred to glycerin according to the modified De Grisse method. The permanent slides were prepared. The nematodes were identified by light microscopy and drawing tube based on their morphologic and morphometrical characters. In this study, the genus Helicotylenchus was the most diverse and abundant with 12 species. Helicotylenchus is a genus of nematodes in the family Hoplolaimidae. Species ars as fallow: H.falcatus , H.urobelus , H.abunaamai, H.insignis, H.morasii, H.conicephalus , H.egyptiensis , H.pseudorobostus , H.californicus , H.crenacauda , H.thornei , and H.pisi. the species were reported, H.urobelus, H.morasii, H.thornei , H.pisi ,H.angularis , as new record for the nematode fauna of Iran. H. morasii is similar to H. abunaamai and H. elegans. It differs from H. abunaamai, in having shorter spear and inner incisures meeting in the posterior quarter of tail kngth (in H. abunaamai, spear = 24-27µm, inner incisures on tail fuse in posterior two-thirds of tail region). It differs from H. elegans in having longer body (0.64mm) , shorter spear (20-18 µm ) and posterior location of orifice of dorsal oesophageal gland (in H. elegans, L = 400-450µm; spear = 21-24µm and dorsal oesophageal gland opening 9-10 µm from spear base). H.pisi Characterized by conical, anteriorly blunt lip region, with three or four cuticular rings; outlet of dorsal esophageal gland situated in esophageal lumen 14 p.m behind base of stylet and tail with 12 cuticular rings on ventral side and ventral outgrowth on terminus. H.urobelus differentiated from its closest relative, Helicotylenchus erythrinae, by the more prominent ventral tail projection and narrow annules on the tail end of the female. H.angularis is unique in the genus in having an angular lip region.H.thornei characterized by absence of cuticular annulations in lip region and presence of tapering tail.