To determine the composition and temporal stability of the gut (faecal) microbiota of sheep (Ovis aries).Microbial population dynamics was conducted using ARISA (28 sheep) and 16S rRNA sequencing (11 sheep). Firmicutes and Bacteroidetes were the predominant bacterial phyla, constituting ~80% of the total population. The core faecal bacterial microbiota of sheep consisted of 67/136 detected families, and 91/215 detected species. Predominant microbial taxa included Ruminococcaceae, unassigned families in Bacteroidales and Clostridiales, Verrucomicrobiaceae and Paraprevotellaceae. Diversity indices and core microbiota composition demonstrated the stability of the core microbiota over 2-4 weeks. The core microbiota remained similar over ~5 months.Temporal stability of the sheep microbiota is high over 2 - 4 weeks in the absence of experimental variables. The core microbiota of Merino sheep shares taxa found in other breeds of sheep and other ruminants.Numerous studies seek to investigate the impact of experimental variables on gut microbiota composition. To do so, knowledge of the innate stability (or instability) of the microbiota over an experimental time-course is required, independent of other variables. We have demonstrated high stability of the gut microbiota in sheep over 3 - 4 weeks, with moderate stability over ~5 months.