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Quaking aspen (Populus tremuloides) is the most widely distributed tree specie in North America. It provides habitat for wildlife, improves water retention, and supports high levels of biodiversity. Browsing by ruminants is likely a key factor inhibiting aspen regeneration, but evidence indicates that not all aspen clones are equally susceptible to herbivory. Aspen produces chemicals, phenolic glycosides (PG) and tannins, which have been shown to deter herbivory and may affect intake of and preference for aspen leaves. We conducted two trials to determine 1) the effect of PG and tannins on intake of aspen leaves by sheep and 2) the preference for aspen leaves by sheep when offered with a forb (Utah pea; Lathyrus pauciflorus), and a grass (smooth brome; Bromus inermis); forages that may grow in the understory of an aspen stand. Poor intake of aspen leaves by sheep indicates plant secondary compounds likely regulate aspen intake. During the preference study, sheep ate all three forages, but preference for aspen increased by September. However, their preference for aspen was highly variable. Individual intake of aspen by sheep was also highly variable and persisted throughout the growing season. Young aspen trees produce very little forage dry matter. Based on our results, ruminants can consume a large number of aspen suckers even if aspen leaves only make up a small percentage of the diet.