Wilt of water melon, caused by Fusarium oxysporum f. sp < em> niveum, is one of the most important economic diseases, which attacks watermelon in any stages of plants development causing great losses under open field.  Fusarium spp. was the most prevalent fungi isolated from watermelon seeds samples followed by Aspergillus spp., Penicellium spp. and other field fungi. Highest percentage of infection and disease severity were recorded in new reclaimed land in El-Gamalia and Sherbeen district in Sandy soil. Different isolates of F. oxysporum f. sp. niveum caused percentage of wilt from 10 % to90 %.  Total count microorganisms in watermelon rhizosphere at maturity stage very high compared with control. All watermelon cultivars were infected with F. oxysporum f. sp. niveum Charleston gray; Giza 1 and Dixie Queen were more susceptible cultivars, while Bicok 60 and Giza 2 were more resistant.