Rosa . an ornamental plant that belongs to Rosaceae, which has many species and cultivars containing Ramblers, Bushes, Dwarf and Miniaturs. Roses are the most important cut flowers and also they are widely used in the landscape. Pruning is one of the factors that affects growth and flowering in roses. Generally the main reason for pruning is to control the growth, flowering and fruit productin in different plants which is done by cutting shoot in correct location. Many studies have outlined the outcome of pruning on fruit production and flowering in greenhouses. This experiment was conducted to study the effect of time and severity of pruning on quantity and quality of rose flowers in field condition and investigate the physiological process. A factorial experiment based on a randomized complete block design (RCBD) was conducted in Isfahan University of Technology between 2014- 2015. Treatments include two levels of intensity and time of winter pruning (remaining five buds in 4 hyhyhyhy; th February and as medium pruning and remaining two buds in 4 hyhyhyhy; th February and 6 hyhyhyhy; th March as heavy pruning), and summer pruning (flower pruning and control), in three replications. Each replication contained two pots Data analysis showed that, heavy pruning in 4 th February increased the number of flowers, flower diameter, the length of flower stem and the number of leaves in flower stem. Summer pruning increased in the number of flowers in spring and summer, also increased the length of flower stem and the number of leaves in summer. Late and heavy pruning in 6 hyhyhyhy; th March delayed the flower initiation. Pruning decrease carbohydrate content in comparison with non-pruned ones. Intensity and time of pruning didn’t make significant differences on nitrate reductase activity. In addition heavy pruning improved photosynthesis efficiency by increasing light penetration in plant canopy. To sum up results suggested that heavy pruning in 4 th February was the best time and severity of pruning for floribunda roses cv “ Ice berg”. Keywords : winter pruning, summer pruning, photosynthesis, soluble sugar.