An outbreak appeared in kingdom of Saudi Arabia in February, 2007 and characterized by high mortalities and some abortions among sheep was studied. Trials for identify the cause of this outbreak were done by performing some traditional diagnostic tools like enzyme linked immunosorbent assay (ELISA) and virus isolation (VI), in addition to using of Reverse Transcription-Polymerase Chain Reaction (RT-PCR) as a recent technique. These assays were performed two successive times one week apart to 100 sheep, 50 of them were suffered from clinical signs and 50 were apparently healthy. All examined animals were negative for first ELISA while Rift Valley Fever virus (RVFV) was isolated from 61 animal in first virus isolation and RVF viral nucleic acid was detected in 68 animals after applying first RT-PCR. IgM antibodies to RVFV were identified in 58 animals with second ELISA while results of virus isolation and RT-PCR remained without change. Results of this work showed that RT-PCR was more sensitive than ELISA and virus isolation while virus isolation was more sensitive than ELISA. RT-PCR and virus isolation could detect early RVFV infection while ELISA failed to detect early infection. This is the third recording of RVF outbreak in Jizan (Southern region of Kingdom of Saudi Arabia) since 2000 when the disease reported for the first time in Kingdom of Saudi Arabia but it is the first to record the outbreak away from rainy season (August-November) and mosquitoes. Some apparently healthy sheep gave positive results with 2nd ELISA (8), with 1st and 2nd virus isolation (11) and with 1st and 2nd RT-PCR (18).From the results of this work I can conclude that RT-PCR is the best available test for diagnosis of early infection of RVF and can be used also in detection of apparently healthy infected animals. Repeated occurrence of RVF outbreaks with the circumstances observed in the last outbreak may proved that the disease became endemic in Kingdom of Saudi Arabia so, it will be the first endemic area outside Africa continent.