Since 1866, large quantities of endophytes with metabolic activity have been isolated from almost all kinds of plants including trees, shrubs, grasses, and even from algae, moss and ferns. The grass endophytes and their hosts are mutualistic symbionts which differ from other endophytes. Studies on Neotyphodium endophytes and grasses indicate that the endophytes can not only protect the host grass from abiotic stresses but also enhance its resistance to biotic disturbances, such as herbivores and pathogens. Up to now, most research on the pathogen resistance ability of endophytic fungi has focused on endophytes isolated from non-grass medicinal plants. As for grass endophytes, limited studies have reported that endophyte-infected grasses are less frequently infected by pathogen disease. Was the resistance from endophytes themselves or from the interaction of the grass-endophyte associations? To address this question, this experiment was performed with isolated endophytes in vitro. In this paper three endophytes were used, i.e., Neotyphodium sp., N. coenophialum and N. lolli. They were isolated from Achnatherum sibiricum (L.) Keng (a native grass which was widely distributed in the Inner Mongolian Plateau), Festuca arundinacea Schreb and Lolium perenne L (cultivated grasses which were widely grown in north China lawns), respectively. Five turf grass pathogens were chosen, i.e., Fusarium sp., Rhizoctonia sp., Cladosporium sp., Phomopsis sp. and Curvularia sp., antagonistic interaction experiment, spore germination experiment and micro-cultivation experiment were carried out to address if the endophytes could resist pathogen fungi in vitro. If this is the case, what kind of antagonistic mechanisms might be involved? The results showed that endophyte Neotyphodium sp. was antagonistic to Cladosporium sp., Curvularia sp. and Phomopsis sp., and the inhibition percentages were 70.1%, 52.3% and 30.9%, respectively, after three days of inoculation. The possible mechanism involved is thought to be competitive advantage of the endophytes for nutrition and super-parasitism. The endophyte N. coenophialum had an inhibitory effect to some extent against Cladosporium sp., while N. lolli appeared to have no inhibitory effect against any of the pathogens. When N. lolli was inoculated with the pathogens, it turned brown while the pathogens took up nutritious space. The results demonstrate that Neotyphodium sp. is more antagonistic to pathogens than N. coenophialum and N. lolli, thus being beneficial to its host grass in pathogen resistance.