Epichloe endophytes growing symbiotically in the above-ground parts of tall fescue increase tolerance of the host plant to a range of biotic or abiotic stresses and also makes the plant more efficient in seeds and forage production. Since Tall Fescue is an open-pollinated plant with gametophytic self-incompatibility system, there are major changes in genotype of the plants from one generation to the next. These changes can affect the compatibility of the plant toward the endophytic fungi. This research was conducted in three different experiments considering the fact that there is no information regarding the amount of transferability of endophyte fungi from the maternal plant to the next generation progenies and also the effects of the maternal and paternal characteristics on the stability of the symbiosis. In the first experiment, 19 genotypes of tall fescue including 11 foreign clones and 8 Iranian clones were investigated for seed production as a result of self and open pollination. . The effect of pollen grain genotype coming from paternal plant on transferability of endophyte to the next generation progenies was also investigated. In this experiment, presence of endophytic fungi at three different positions (top, middle and bottom) on the inflorescence of maternal plants, 75C+ and 75B+ were traced. Also endophytic fungi were detected in three ovaries in each position at two different times. In the third experiment, first of all, the resultant seeds from the crosses in the second experiment were germinated in the sterilized petri dishes. Then, seedlings which had grown in the pots, were separated from their endosperm and were tralanted in the field. Seedlings were planted in a randomized completed block design with three replications in order to investigate the genetic differences made by the cross of paternal and maternal parents of tall fescue in the half-sib populations. The results of the first experiment showed that the phenotypic variation among tall fescue genotypes was decreased due to increasing the similarities between endophyte-infected 75B and 75C and those genotypes without the endophyte, especially those with foreign origin. In the first experiment, endophyte-free genotypes of 75B- and 75C- had lower mean than other foreign and Iranian genotypes regarding the characteristics such as the number of seeds in open-pollinated panicles, the number of seeds in self- pollinated panicles, selfing ratio, 100-seed weight in self-pollinating seedheads, 100-seed weight in open-pollinated seed-heads, seed yield in self- and open-pollinated panicles. However, endophyte-infected genotypes of 75B+ and 75C+ had higher means than those of foreign genotypes. Also, two clones of 75B+ and 75C+ had higher rate of selfing in compression with those with no endophytes. Thus, it seems endophyte fungi decrease the host self-incompatibility by hormonal change in tall fescue panicles and increase self-fertility. Survival assessment of the pollen grains which is done by the three methods of Aniline blue, Iodide and Tetrazolium, showed that those pollens collected from endophyte-infected plants, especially 75B+, had around 70% chance of survival after 3 days, while the chance of survival in of endophyte-free clones was zero. Therefore, the possibility of seed production increases in plants havin endophyte especially via self-pollination. These results showed that since the endophytic fungi are located in inner tissue of the host plant, probably environmental factors do not have an effect on endophyte abortion and only foreign pollens may change the presence of endophytes. Although it was clear that the intensity of the presence of endophytic fungi in seedlings is extremely dependent to its presence in the seed, the intensity of this correlation decreased probably due to the effect of paternal pollen. The results of the third experiment showed that the variation in progenies due to the effect of maternal parent, 75B+ and 75C+ for days to spike emergence, vegetative height, generative height and plant diameter was more than the effect of paternal genotypes which shows the dominant effect of maternal alleles appearing in progenies. Considering the genetic diversity caused by the crossing, it seems that foreign clones, Silverado and Monarch, are proper genotypes for crossing to make a population and choosing the best plants after the crossing with the genotypes of 75B+ and 75C+. Also, considering the characteristics of parents and progenies made by the cross, it seems that the genotype 75B+ and its progenies are suitable to be used as lawn and the genotype 75C+ and its progenies are suitable to be used for forage production. Keywords: Endophyte, tall fescue, transferability, inheritance, stability