Decreasing vegetative growth and controlling plant height is one of the most important aspects of the production of some ornamental plants. To study the role of uniconazole and cycocel on some morphological and biochemical characteristics of F2 petunia seed cv. haun xiang, a factorial experiment was conducted in a completely randomized design using five replications at sari agricultural sciences and natural resources university. The first factor was plant growth retardants of uniconazole (0, 5 and 10 mg L-1) and cycocel (0, 1000 and 1500 mg L-1), and the second factor was application type (leaf spraying and soil use). The studied traits were plant height, lateral branch number, flower number, flower diameter, budding time, peroxidase (POD) and superoxide dismutase (SOD) enzyme activity, endogenous gibberellins, total anthocyanin and total phenol content. The lowest plant height and gibberellin were observed in uniconazole 5 and 10 mg L-1. The highest number of flowers, enzyme activity was in 10 mg L-1 of uniconazole in soil use. The treated plants with 5 mg L-1 of uniconazole produced the highest flower diameter and total phenol. The onset of flowering was observed at 1500 mg L-1 of cycocel. According to the results of this study, for improving the vegetative and flowering characteristics of petunia seed, the use of 5 and 10 mg L-1 of uniconazole as soil use and spraying with 1500 mg L-1cycocel is recommended