Achnatherum sibiricum is a perennial sparse bunchgrass native to the Inner Mongolia Steppe of China, and it is highly infected by Epichlo /Neotyphodium fungal endophytes. Early studies of grass endophyte associations suggested that endophytes were plant-defending mutualists. For native grass endophyte associations, however, their interactions are more variable. The symbiosis between endophytes and their natural hosts have been suggested to range from antagonistic to mutualistic. In some grass species, endophyte infection could benefit their hosts under stress conditions, while in other studies, endophyte-infected (E+) grasses did not appear to be competitive over those that were endophyte free (E-). It was reported that in native grass populations, endophytic fungal communities may be more diverse and variable than that of agronomic and economically important species. It was also reported that plant genotype had been shown to interact with environmental factors in altering performance of Neotyphodium-infected tall fescue and perennial ryegrass, at least relative to drought tolerance or soil nutrients. What is the effect of the different endophyte species? In our pervious study, we controlled all conditions except endophyte species. Two endophyte species, Neotyphodium sibiricum (K) and Neotyphodium gansuence (M) were isolated and identified from A. sibiricum. In the present study, the effect of the two different Neotyphodium species on growth and photosynthetic characteristics of A. sibiricum was carried out. The results showed that there were no significant difference in the percent of nitrogen content between E+ and E- plants.The trend of the leaf mass per area (LMA) had gradually increased between E+ and E-, but the difference was not significant. Similarly, the photosynthetic nitrogen use efficiency (PNUE) between E- and E+ also had no significant difference, and there were no significant differences in the PNUE of K and M. The above ground and root biomass of E+ tended to be higher than those of E-, only the difference was not significant. As for K and M, no difference occurred in biomass distribution, plant height, leaf number, as well as tiller number. The light curve showed that the net photosynthetic rate was E- >K > M. The CO₂ compensation point of E- plants was significantly higher than that of E+, which indicated that E+ plants had higher CO₂ utilization efficiency than E- plants. Different endophyte species had no significant effect on the CO₂ compensation point of A.sibiricum. However, our results suggested that the CO₂ compensation point was much more variable in E+ and E-, and the transpiration rate and stomatal conductance of E+ were significantly higher than those of E-. Thus, it was beneficial to the plant when stomata was almost closed, which promoted E+ to use the low CO₂ concentration more efficiently. In brief, different endophyte species had no significant effect on growth and photosynthetic characteristics of A. sibiricum in this study. We speculated that different species of endophyte maybe have different effects on A. sibiricum depending on the host genotype and growing conditions. These effects had yet to be studied further.