Although Arabian horses have been bred in strains for centuries and pedigrees have been recorded in studbooks, to date, little is known about the genetic diversity within and between these strains. In this study, we tested if the three main strains of Syrian Arabian horses descend from three founders as suggested by the studbook. We examined 48 horses representing Saglawi (n = 18), Kahlawi (n = 16) and Hamdani (n = 14) strains using the Equine SNP70K BeadChip. For comparison, an additional 24 Arabian horses from the USA and three Przewalski's horses as an out group were added. Observed heterozygosis (Ho) ranged between 0.30 and 0.32, expected heterozygosity (He) between 0.30 and 0.31 and inbreeding coefficients (Fis) between −0.02 and −0.05, indicating high genetic diversity within Syrian strains. Likewise, the genetic differentiation between the three Syrian strains was very low (Fst < 0.05). Hierarchical clustering showed a clear distinction between Arabian and Przewalski's horses. Among Arabian horses, we found three clusters containing either horses from the USA or horses from Syria or horses from Syria and the USA together. Individuals from the same Syrian Arabian horse strain were spread across different sub-clusters. When analyzing Syrian Arabian horses alone, the best population differentiation was found with three distinct clusters. In contrast to expectations from the studbook, these clusters did not coincide with strain affiliation. Although this finding supports the hypothesis of three founders, the genetic information is not consistent with the currently used strain designation system. The information can be used to reconsider the current breeding practice. Beyond that, Syrian Arabian horses are an important reservoir for genetic diversity.