The effects of potassium sulfate application on the quantitative and qualitative yield under water deficiency on Brassica napus Var RGS003 were evaluated in the Research Field of Collage of Agriculture, Zabol University in 2010-2011, on the basis of a split plot with basic design of Completely Randomized Block in three replicates. In this experiment, there were 3 type of irrigation, complete irrigation, halted irrigation at pollination stage, and from start of grain filling as main plot and potassium sulfate treatment included: 0, 50, 100 and 150 Kg/ha which is applied at sowing time as subplot. The results show that the irrigation stoppage had significant effect on grain yield, oil percent, oil yield, and proline content at statistically level (P>0.01). The most of all of these characteristics obtained from complete irrigation. For potassium treatment the most of grain yield, oil yield, and proline obtained from 150 Kg/ha. The final results show that 50-100 Kg/ha potassium sulfate and usually irrigation increase the yield of Brassica napus in Sistan region.