Drastic seasonal changes in higher latitudes and altitudes impact the phenology of plant growth forms differently and thus diet of ungulates feeding on them. We examined how fecal nitrogen (N), an indicator of diet quality, varied with season against the background variation in forage biomass and N in habitats of two sympatric ungulates in subtropical Himalaya. We conducted this study in Kyongnosla Alpine Sanctuary, Sikkim, where the Himalayan goral Naemorhedus goral occurred from 3000 to 3600 m and Himalayan musk deer Moschus chrysogaster from 3300 to 4200 m. We measured biomass and N content of forbs and graminoids and browse in their habitats and proportions of monocots and dicots and N content in their fecal pellets. Seasonal variation in biomass, primarily determined by forbs, was similar in goral and musk deer habitats. Goral had a graminoid-dominated diet switching to dicots in autumn and winter. Musk deer had a dicot-dominated diet in all seasons. Fecal N in both the ungulates was higher than forage N in all seasons except spring when the latter was greater. Forage and fecal N declined sharply from spring as seasons progressed. Fecal N in goral was considerably lower than in musk deer in all seasons, probably below maintenance levels in autumn and winter. As evident from peaks and duration of high diet quality, goral is likely a capital breeder and musk deer an income breeder. Results suggest that linkages between diet and reproductive seasonality in ungulates will have important implications in face of climate change.