Wild ruminants may differ in their protozoal fauna according to their feeding type, but a comprehensive evaluation of available data is lacking. Here, we evaluate the literature data available on the protozoal fauna (diversity, concentration and proportions of the major groups including Entodiniinae, Diplodiniinae and Isotrichidae) in relation to the natural diet (as percentage of grass in the natural diet, %grass) and body mass (BM) in 55 wild ruminant species. The effects of ruminant phylogeny were controlled for using phylogenies based on molecular data and phylogenetic generalized least-squares. Transferring results from domestic to wild ruminants, we hypothesized (1) a decrease in the proportion of Entodiniinae and an increase in that of Diplodiinae, with %grass in the natural diet; (2) a positive correlation between Diplodiinae and Isotrichidae; (3) no influence of BM on these protozoal groups. Based on the literature statements, we additionally expected that (4) protozoa diversity increased with %grass and BM and that (5) protozoa concentrations were independent of both BM but decreased with %grass. Only hypothesis 1 was confirmed completely. Isotrichidae and Diplodiinae only tended to correlate (P=0.08), but the proportion of Isotrichidae increased with BM. Protozoa diversity only increased with BM but not with %grass. Protozoa concentrations were very variable across the %grass range but in extreme grazers, only low concentrations were reported. The results indicate that diet determines protozoa concentrations and part of the taxonomic composition of the protozoal fauna, but not protozoal diversity. Yet, conditions determining the protozoal fauna have not been completely understood; in particular, conditions relating to the presence of Diplodiinae and Isotrichidae, which occur in opposing magnitudes in wild and domestic ruminants, respectively, remain to be investigated. The results indicate clear effects of the ecology of host species (BM, natural diet) on the ecology of their protozoal endobionts.