Abstract: Agriculture is the backbone of Pakistan. It is very important to promote the crops meet food requirements of the growing world population. A field experiment was conducted to study the effect of deficit irrigation and nitrogen levels on growth and yield of cauliflower under drip irrigation at research farm, The University of Agriculture Peshawar, Khyber Pakhtunkhwa. The experiment was performed in the growing season of cauliflower, i.e, October 2014-January 2015. The experiment was designed on split plot arrangement (RCBD) having three replications. There were two factors, irrigation and nitrogen. Four irrigation and three nitrogen levels and their interaction were studied. Irrigation was applied as I₁ was 100% of full irrigation (MAD), I₂ was 75% of full irrigation, I₃ was 50% of the full irrigation and I₄ was 25% of full irrigation. Fertilizer nitrogen was applied as N₁ was 20 kg/ha, N₂ was 40 kg/ha and N₃ was 60 kg/ha. Drip irrigation system of emitter spacing of 40 cm and the lateral spacing of 45 cm was being installed at the field of experiment. The length of lateral was 10 m. Area of the experimental field of single replication was 54 m² (10H5.4 m). Total numbers of the experimental units were 36 and area of one plot was 4.5 m². Soil moisture content was determined by volume basis before sowing and then by Frequency Domain Reflectometer (FDR) at daily basis. Different insecticides were sprayed in the field for elimination of different insects. Agronomic practices were done in the field for bitter crop production. Irrigation levels were applied as I₁-I₄ that were 100, 75, 50 and 25% of full irrigation respectively. Each plot was irrigated by their exact calculated time by the drip irrigation method. Daily rainfall data during research period was recorded. Nitrogen levels were applied as N₁- N₃ that were 20, 40 and 60 kg/ha, respectively. Results showed that different irrigation levels significantly affected number of leaves per plant, leaf length, leaf weight, plant height, days to curd initiation, days to curd maturity, curd diameter, biological yield, curd yield, water use efficiency and harvest index. Maximum number of leaves per plant (23), leaf length (29 cm), leaf weight (457 g), plant height (59 cm), days to curd initiation (93), days to curd maturity (16), curd diameter (27 cm), biological yield (50 ton/ha), curd yield (41 ton/ha), harvest index (8.50%) and water use efficiency (201 kg/ha mm) was recorded. The irrigation levels, nitrogen levels and reduction in irrigation brought significantly affected the number of leaves per plant, leaf length, leaves weight, plant height, curd diameter, biological yield and days to curd initiation, days to curd maturity and curd yield. Higher levels of irrigation and nitrogen recommended may be applied to assess the future highest production.