Using medicinal plants dates back to prehistoric times. Oilseed pumpkin is an introduced medicinal plant that seeds and some other organs of which are being hired for treating an array of human diseases in Iran. Considering its significance in the health products industry, the countrywide drought stress and a lack of information on mineral nutrition of oilseed pumpkin, the present study was aimed at studying the impact of irrigation regime and N application on chlorophyll (Chl) content, gas exchange properties, proline content, yield and yield components of this medicinal plant. A 5-replicate split plot, randomized complete block experiment was conducted at the Lavark Research Farm, College of Agriculture, Isfahan University of Technology-Isfahan, Iran at 2009. Three irrigation regimes based on evaporation from a ), 95 mm (I 2 = moderate water deficit) and 130 mm (I 3 = severe water deficit) were assigned as main plots. Three nitrogen (N) application rates including zero N (N 1 = control), 120 N (N 2 ) and 220 N (N 3 ) kg ha -1 N as urea chosen as subplots. Leaf area index (LAI), gas exchange attributes, Chl and proline content, fruits/plant, seeds/fruit, 1000-seed weight, fruit and seed yields, oil content and yield were measured. I 1 and I 3 irrigation levels with 2.11 and 1.46 and N 3 and N 1 nitrogen levels with 2.50 and 1.16 produced the greatest and smallest LAI, respectively. Water deficit stress and lowered N application led to significant decreases in leaf Chl content. Water deficit led to decreases in the net photosynthetic rate (A) and leaf stomotal conductance (gs) but it led to increases in internal Co 2 concentration (C i ). While A and gs increased with N application rate, but C i decreased with the increace in N application. Proline content increased with both increase in water deficit stress and N application rate. I 3 irrigation level led to 23, 33, 5, 51, 52 and 55 percent decreases in the fruits/plant, seeds/fruit, 1000-seed weight, seed and fruit yield and oil yield, respectively, compared to the I 1 level. N 3 level of nitrogen application resulted in 28, 22, 27, 9 and 33 percent decreases in fruits/plant, fruit and seed yield, oil percent and oil yield, respectively, compared to the N 1 level. It could be concluded that the negative impact of water deficit stress on yield and its components in oilseed pumpkin is mainly through the decreases in the photosynthetic surfaces and rate and chl content. Furthermore, application of 220 kg ha -1 N may lead to increases in LAI, Chl and A, though the latter increases, seemingly, enhance the growth of vegetative organs rather than reproductive and grain yield components. Keywords : oilseed pumpkin, water deficit, N