Five stigmaeid species belonging to the genus Agistemus Summers (Acari: Trombidiformes: Stigmaeidae) are recorded from different regions of Saudi Arabia. Among these, Agistemus jawadi sp. nov., inhabiting on Ziziphus spina-christi (L.) Desf. is described and illustrated based on female. Two species, A. fleschneri Summers and A. aimogastaensis Leiva et al. are recorded as new to the fauna of Saudi Arabia. Two species A. fleschneri and A. exsertus Gonzalez-Rodriguez are re-described based on adult females. Moreover, Agistemus species are categorized in two species groups;fleschneri and terminalis based on one and two pairs of aggenital setae respectively. A key to the world species of the genus Agistemus is provided. Three species, Agistemus rafiqi Khan et al., A. rawalpindiensis Khan et al. and A. layyahensis Khan et al. are considered as junior synonyms of Agistemus garrulus Chaudhri et al. 1974.