In the present study, we explored the perceptual span of skilled Uighur readers during their natural reading of sentences. The Uighur script is based on Arabic letters and it runs horizontally from right to left, offering a test to understand the effect of text direction. We utilized the gaze contingent moving window paradigm, in which legible text was provided only within a window that moved in synchrony with readers’ eyes while all other letters were masked. The size of the window was manipulated systematically to determine the smallest size that allowed readers to show normal reading behaviors. Comparisons of window conditions with the baseline condition showed that the Uighur readers reached asymptotic performance in reading speed and gaze duration when windows revealed at least five letters to the right and twelve letters to the left of the currently fixated one. The present study is the first to document the size of the perceptual span in a horizontally leftwards running script. Cross-script comparisons with prior findings suggest that the size of the perceptual span for a certain writing system is likely influenced by its reading direction and visual complexity.