The characteristics of the leaf epidermis of the main monocotyledonous plant species from grasslands on the Tibetan Plateau were investigated using optical microscopy. The differences in stoma quantitative indices among plant species was studied using one-way ANOVA and the relationships between stoma quantitative indices and environmental factors, such as altitude, and average temperature and precipitation in the growing season, were analyzed using the Pearson correlation and linear regression analysis. The results indicated that:(1) The main monocotyledonous plant species on the grassland shared many special leaf epidermis characteristics, due to long-term adaptation to the plateau environment. These characteristics included:(a) Two types of cells on the leaf epidermis:long cells were generally rectangular and closely arranged in rows; and short cells were rectangular, square, suborbiculate, or saddle-shaped, and their distribution was randomly scattered, solitary, or twinned among species. (b) Most stomas were distributed in the lower epidermis and belonged to the single-sided type. This pattern might play an important role not only in maintaining high CO₂ assimilation rates but also to limit water evaporation and avoid physiological drought. (c) Morphologies of stomatal apparatus, guard cells, and subsidiary cells showed obvious polymorphism. Guard cells were nearly square, half-moon, or dumbbell-shaped. Subsidiary cells were low-dome, dome, or high-dome shaped. The stomatal apparatus appeared in an ellipse, wide-ellipse, or intimate circle. (d)The stomatal apparatus was paracytic, containing two guard and two subsidiary cells, and was further aligned into stomatal bands with equal or unequal intervals. Subsidiary cells were surrounded by and parallel to guard cells. (2) Average stomatal density (SD), length (SL), and index (SI) were (194.07±4.74) units/mm², (34.50±0.28) μm, and (18.13±0.31)%, respectively. The coefficient of variation (CV) of SD (53.02%) was largest, followed by those of SI (37.23%), and SL (17.94%). There were significant differences among species in these three stoma quantitative indices (P<0.01). (3) Stoma quantitative indices of monocotyledonous plants of grasslands on the Tibetan Plateau were distinctly correlated with environmental factors. Altitude was significantly associated with stomatal characteristics of the leaf epidermis (P<0.01). Average temperature in the growing season had a weak positive correlation with SL (P<0.05), and a notable negative correlation with SD and SI (P<0.01). Precipitation in the growing season was significantly negatively correlated to SI (P<0.01). Specifically, SL, SD, and SI increased with increasing altitude; SL decreased, and SD and SI increased as average temperature in the growing season decreased; SL increased, and SD and SI decreased with reduced precipitation in the growing season. (4) The linear regression equations of SL, SD, and SI from altitude, average temperature, and precipitation in the growing season were Y=0.005X₁+0.878X₂-0.021X₃+12.278; Y=0.046X₁-11.688X₂+0.466X₃-46.391; and Y=0.003X₁-0.363X₂+0.009X₃+7.394, respectively, which were extremely significant (P<0.01). The relationship between environmental factors and the leaf epidermis characteristics showed that the coefficient of SD was the largest (R=0.690), followed by those of SL (R=0.557), and SI (R=0.342).