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Sarcocystis infections are common in domestic and wild animals. Pathogenic species are a cause of serious economic losses of livestock. In wild animals, infections with these parasites and their negative impact on wild populations are ill studied. The aim of this study is to determine the prevalence of Sarcocystis infections in gazelles kept at the King Khalid Research Centre (KKWRC), Saudi Arabia, and to establish the specific identity of the parasites causing these infections. This study was also designed to determine the definitive host(s) in which the sexual stages of the life cycle develop. Determining the definitive host of Sarcocystis species that infect gazelles may help in controlling the parasites. This study was also intended to examine the phylogenetic relationships between Sarcocystis parasites from different gazelle species, using modern techniques that involved the polymerase chain reaction (PCR) and sequencing the 18S rRNA gene. The prevalence of Sarcocystis infections in gazelles from Saudi Arabia was by macroscopic and microscopic (histological and peptic digestion) No macroscopic sarcocysts were found but Sarcocystis parasites were 66.7% of gazelles investigated by pepsin digestion and 39.9% using histological examination. Gazella dorcas showed the highest prevalence (83.9%) using the digestion technique, followed by Gazella subgutturosa marica (74.3%), Gazella thomsoni (55.6) and Gazella gazella (54.9%). The lowest prevalence was recorded from Gazella erlangeri (35.7%). A significantly higher prevalence rate was reported from from KKWRC main enclosure compared with those in the new breeding pens. Infection was significantly higher in adult gazelles compared with juveniles. The Arabian red fox (Vulpes vulpes arabica) was determined to be the definitive for Sarcocystis parasites in G. gazella and G. s. marica, through experimental Gazella gazella was also reported to act as an intermediate host for the cyst-forming coccidium, Hammondia heydorni and the Arabian red fox was found to act as a definitive host for the same parasite. The identity of Sarcocystis parasites detected in gazelles was determined using light and transmission electron microscopy. Microscopic characterisation showed five distinct species of Sarcocystis, which were subsequently described. However, sequence analysis of the 18S rDNA of Sarcocystis parasites reported from gazelles indicated that they were genetically identical in this region of the genome with the exception of that species derived from G. thomsoni. Sequence data also indicated that the group of Sarcocystis parasites detected from gazelles clustered with those species known to utilise canines as their definitive hosts.