The objective of this study was to evaluate changes in ruminal protozoa in lambs after partial replacement of feed concentrates in their diets with Gliricidia sepium silage. Twenty-four male Santa Ines lambs with an average initial weight of 14.5 kg were used. The experimental design was completely randomized, with four treatments and six replications. Treatments (given as a percentage of dry matter) were as follows: control -corn silage (600 g kg −1 as fed) + concentrate (400 g kg −1 as fed); GS133 -corn silage (600 g kg −1 as fed) + G. sepium silage (133 g kg −1 as fed) + concentrate (267 g kg −1 as fed); GS267 -corn silage (600 g kg −1 as fed) + G. sepium silage (267g kg −1 as fed) + concentrate (133 g kg −1 as fed); and GS400 -corn silage (600 g kg −1 as fed) + G. sepium silage (400 g kg −1 as fed). Samples of rumen contents were obtained at slaughter, and analysis revealed the presence of nine genera of rumen protozoa that were present in all animals, with the exception of Enoploplastron and Eremoplastron. There were no significant differences in the average total numbers of rumen ciliates or in the composition of species between lambs. Inclusion of up to 400 g kg −1 (as fed) G. sepium silage in the diet of lambs does not affect the diversity or density of rumen protozoa.