Two field experiments were carried out at Sakha Agricultural Research Station during the 2009 and 2010 seasons to investigate the impact of water stress treatments (40, 60 and 80% depletion from available soil water) and potassium fertilizer levels (18, 24 and 30kg K₂O/fed) as potassium sulphate on the growth, yield and essential oil of fennel plants. The obtained results showed that supplying plants with a water level of 40% from available soil water and 30kg K₂O/fed were effective on raising the productivity of fruit yield and essential oil. The interaction between these two treatments gave the best results. Concerning essential oil constituents, methyl chavicol (estragole) was the major compound, followed by limonene, fenchone, anethole, a pinene, myrcene and b pinene. The values of consumptive use, water applied and water storage in the effective root zone were clearly affected by irrigation treatments where the highest values for the three studied parameters were increased under I₁ (irrigation at depletion of 40% from available water, consequently, the values of these parameters can be arranged descendingly as follows: I₁ > I₂ > I₃ while, the mean values of water application efficiency can be arranged descendingly in order of  I₃ > I₂ > I₁.