Forage samples from fringed sagebrushforbsneedlegrass (mountain steppe) and forbsgrasses (mountain meadow) communities in the forest steppe rangelands of Mongolia were collected in late February, April, May, June, July, August, September and October. Samples were analysed for chemical composition and digestibility. The study indicated that OM content of mountain steppe pasture ranged from 86.3 to 91.7%. The highest value (13.6%) of CP was found at the end of May, and the lowest value (6.6%) was found in October. Organic matter digestibility ranged from 46.9 to 74.9%. Organic matter content of mountain meadow pasture ranged from 89.9 to 94.1%. The highest value of CP was found at the end of the May (18.2%), and lowest value (7.9%) was found in April. Organic matter digestibiity ranged from 43.5 to 67.6%. Mountain steppe communities showed higher digestibilities and lower CP, compared to mountain meadow communities, except in late April. New growth of the mountain steppe communities begins around 10th of April. Therefore these communities were better both in CP and energy value compared to mountain meadow communities in which new growth usually begins in the first 10 days of May.