The compression behavior of Nickel has been studied to test the validity of fundamental equation of state. To validate our results five fundamental equation of states (viz. Murnaghan EOS, Birch EOS, Usual-Tait EOS, Kholiya EOS and Vinet EOS) are used to compute the pressure upto the compression ratio of 0.8286. In the present work it is observed that the result obtained for Nanocrystalline Nickel by using Murnaghan, Usual Tait and Vinet equation of state are consistently very close and in good agreement with the experimental results. However the results obtained by using Murnaghan equation of state are very close to the experimental values at higher compression but not consistent in the lower range of compression. The validity of Kholiya equation of state is limited to the lower compression range only while the Birch equation of state has no agreement with the compression behavior of Nanocrystalline Nickel (n-Ni). With the validity of Usual- Tait equation of sate for n-Ni the variation of isothermal bulk modulus of the sample has also studied and found its linear variation with pressure.