We have made a systematic study of the electric dipole moment (EDM) of neutron Dn in various models of CP violation. We find that (i) in the standard KM model with 3 families, the neutron EDM is in the range 1.4 × 10−33 ≤ |Dn| ≤ 1.6 × 10−31 e.cm , (ii) the two Higgs doublet model has approximately the same value of Dn as the standard model, (iii) Dn in the Weinberg model is predicted to satisfy |Dn| > 10−25 e.cm , (iv) in a class of left-right symmetric models Dn is of the order of 10−26±1 e.cm , (v) in supersymmetric models, Dn is of order 10−22ϕ e.cm with ϕ being the possible phase difference of gluino mass and the gluino-quark-squark mixing matrix, (vi)the strong CP parameter θ is found to be θ < 10−9, using the present experimental limit that |Dn| < 2.6 × 10−25 e.cm with 90% confidence.