This study for evaluation the effect of some plant growth retardants on growth and development parameters of Dahlia spp. as a completely randomized design experiment with 10 treatments, 3 replication and each treatment with 3 plant, a total 90 pots were conducted. Treatments includ Paclobutrazol with three levels 50, 75 and 100 ppm, Daminozide and Cycocel with three levels 500, 750 and 1000 ppm and the pot was without spraying as a control. Treatments were applied when the plants had 8 to 15 true leaves and after treatments, sampling and evaluation of traits were performed about 60 days after spraying. The studied traits include air and root fresh and dry weight, longest root length, plant length, number of flower, anthocyanins of petals and total chlorophyll of leaf content and flowering period. The results showed that the most of air fresh weight, anthocyanins of petals content and flowering period and the lowest number of flower was in Cycocel 1000 ppm. The most of root dry weight and the lowest plant length was in Paclobutrazol 100 ppm. Also the most air dry weight in Daminozide 750 ppm, the most root fresh weight and longest root length in Paclobutrazol 75 ppm, the most total chlorophyll of leaf content in Daminozide 1000 ppm, the most number of flower in Daminozide 5000 ppm and the most plant length was in control treatment.