Turfgrasses are monocotyledonous plants, from the Poaceae (Gramineae) family and they are one of the major factors in landscape design. Bermudagrass ( Cynodon dactylon ), is one of the most important Turfgrass in warm season and since It is valued for their drought tolerance and salinity. Bermudagrass are frequently used in temperate regions. Bermudagrass also used in transition zone in this plant growth rate was increased in high humidity. low resistance to freezing couses damage to cynodon dactylon cold. This damage will be more intensive in compact areas such us golf ground, low clipping level and heavy traffic. Plant growth regulator have an appropriate role in program turfgrass management.plant growth inhibitors and growth retardants appliction in grasses would reduce the vegetative growth, improve the root density, color quality and would increase the photosynthetic rates, respiration decrease and resistance to biotic and abiotic stresses. Trinexapac-ethyl is one the retardants that used in recent year. Regarding to sensitivity of Bermudagrass to low temperature and its importance in landscape, therefore we studied the effects of different concentrations of Trinexapac-ethyl on the morphological characteristics, increase of cold tolerance in three varieties of Bermuda grass and introduced one variety which has short dormancy duration. So this research was done with split plot factorial in time by Randomized complete block design method with three replications and each replication consist of two pots and three varieties of Bermuda grasses named Regles, Tifway and Tifdwarf, in research-training greenhouses of Agricultural department in Isfahan university of technology. Treatments included four concentrations, 0, 4, 6, 12 (mg/ m 2 ) of Trinexapac-ethyl were used monthly in September, October and November 1388 and from March to October of 1389. During this period, factors such as height, color wet and dry weight were measured regularly. The amount of Proline was measured twice in November months of 1388 and 1389 when weather was getting cold. To study the Rhizomes survival in late January and February in 1388, Rhizomes were transferred to incubator at low temperatures and percent survival of rhizome was measured after get out of the incubator and planting in pots. At the end of the test and after removal of plants from spots, the root densiy, depth, wet and dry weight of roots were measured. Trinexapac-ethyl compared to control, reduced the growth rate and height root in all three varieties, however any significant differences were not observed between these concentrations. The most reduction in grass height was seen in Tifdwarf variety. applictionTrinexapac-ethyl hormones in all three varieties increased the amount of Proline compared to control. Based of this result the Maximum amount