The aim of this study was to investigate the effect of two carbohydrate sources, barley and maize, on the ruminal fermentation of Atriplex nummularia cv. De Kock fed to sheep. Barley was used as a source of rapid fermentable carbohydrates while maize was used as a moderately fermentable source. Ten rumen cannulated Merino wethers were fed different increments of ground maize and barley supplements (0%, 15%, 30%, and 45% of the ration dry matter to a basal diet of A. nummularia over four different periods. Supplementation of A. nummularia with energy tended to increase ruminal fermentation. Rumen ammonia nitrogen (NH3-N) decreased at the 30% level of supplementation, though an increase in rumen NH3-N concentration was observed for maize at the 45% level. This decrease might have been due to an improvement in microbial protein synthesis. Total rumen volatile fatty acids increased with increasing levels of both barley and maize supplementation. Evidence of the increase in volatile fatty acid production was supported by a decrease in ruminal pH values, with the barley at 45% level of supplementation yielding the lowest rumen pH values. Supplementing sheep with barely and maize at 30% level increased fermentation in the rumen of sheep fed on A. nummularia and enhanced utilisation of degradable protein available in the rumen.