Rift Valley Fever (RVF) is acute viral mosquito-borne disease of Ruminants and man that can cause epizootics and associated human epidemics. This study was carried out for detection of RVFV IgG in animals and man and to investigate the occurrence of RVFV in mosquitoes. A total of 460 animal blood samples were collected from vaccinated and non vaccinated sheep (172), goats (48), cattle (164) and buffaloes (76) from different farms, flocks and abattoirs in Menoufia, Behera and Kafr El Sheikh Governorates. All samples were examined by indirect Enzyme Linked Immunosorbant Assay, the overall detection percentages of RVFV IgG antibodies were 14.9% in non-vaccinated animals and 19.2% in vaccinated animals, respectively and it was found that Kafr El sheikh had the higher percentage than the other two Governorates (21.4 %). Also sheep and goat represented the most principle host to RVF by a parentages of 21.4% and 18.7 % respectively, especially on the age group > 3- 5 years by (17.9%). Moreover, female animals had the higher percentage (17.7%) than males (8.6%). Furthermore this study proved that RVF play an important role in abortions especially in sheep and goats. In human, a total of 369 human blood samples collected from fever hospitals and clinical laboratories in the three Governorates. It was found that males contacted to animals such as sheepherders, farmers and butchers showed higher percentage (12.9%) than females, especially in the age group 30-45 years by a percentage of 16.6%. This results potentiate the role of animals in transmission of disease to man. Concerning mosquitoes, a total of 872 mosquitoes were collected by using CDC light trap and identified into 32 mosquito pool according to genus Culex, Aedes and Anopheles, culex constituted the higher percentages of 71.8%. All mosquito samples did not give any band at the expected size 342 bp by RT- PCR. This negative result did not mean that the virus completely absent as might be present in a low level in the study area or might be present in other Governorates in Egypt.