The present study was conducted at the experimental area of Horticulture Research Station at El-Kanater El-Khayria, Qalyubia Governorate, Egypt, throughout two seasons of 2019 and 2020 to estimate water requirement of  Paulownia hybrid T121 seedlings irrigated at three regimes each 3, 5 and 7 days intervals .The obtained results indicated that, all parameters of vegetative growth e.i, seedling height , stem diameter , leaves area, biomass fresh and dry weights significantly exceeded when irrigated each 3 days interval followed by 5 days then 7 days was the latest one. Meanwhile root length was the longest at 7 days interval and the shortest was with 3 days. The amounts of irrigation water applied and water consumption (L/seedling)  increased under irrigation at 3 days intervals since gave the highest significant water applied and consumption  followed by irrigation at 5 days interval, then the latest at 7 days interval. Average of water productivity at 3 days interval declared that, one liter of water applied produced 4.45 and 1.16g biomass fresh and dry weights respectively. While at 5 days it gave 3.99 and 0.98 g in addition, at 7 days interval induced 3.95 and 0.93 g biomass fresh and dry weight during two seasons respectively. Also water use efficiency (WUE) was influenced by different irrigation intervals and the differences between 3 and 5 or 7 days intervals were significant in two seasons due to reduction of biomass fresh or dry weights, furthermore, Paulownia hybrid T121 had taken higher amount of water applied and water consumption but the most has been depleted by higher transpiration without using it in metabolism synthesis. Total chlorophyll was influenced by  different water regimes it is significantly increased at abundance of water at (3 days) intervals meanwhile total carbohydrate and proline content significantly decreased  at  same water regimes  of (3days) and the opposite occurred at water stress of (7 days). The obtained results indicated that, it is not preferable mainly to depend upon Paulownia spp. in setting up forestation schemes owing to poverty of water resources in Egyptian condition. Therefore it can be recommended that economically can depend on another fast-growing timber trees species in a forestation.