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To study the effects of nitrogen fertilizer and irrigation on yield attributes in two winter rapeseed cultivars a field experiment was conducted at Research Farm of
Agriculture College, Karaj in 1997 using a split factorial as complete block design with four replications. Treatments included three irrigation levels (main plot) and a combination of nitrogen fertilizer in three levels and cultivars namely: Ceres and Cobra as factorial (subplot). At harvesting, the grain yield and yield attributes such as pod number, 1000-grains weight, oil percent, etc were determined. The results indicated that nitrogen had a significant effect on grain, oil and protein content, grain protein percent, and pod number. All traits showed increase with increasing levels of nitrogen, except the oil percent which showed a decreasing trend. Nitrogen had a more significant effect on increasing grain yield via pod number increment (P=O.O 1). Irrigation increased oil percent and grain seed weight but decreased grain protein content. There was a negative correlation observed between oil and protein content (P=0.0l). The two rapeseed cultivars exhibited significant differences in traits such as pod number, grain yield, oil yield, 1000 grain weight and plant height.