Abstract: The study of generalized derivations is interesting in the theory of operator. It has developed with strong links to (mathematical) physics and mechanics, and continue to attract both pure and applied mathematicians in its vast area. Generalized derivations have been extensively studied in literature. The generalized derivations are natural objects in operator theory and there are many substantial and attractive results about their properties. The aim of this thesis is to survey some spectral properties of certain classes of nonnormal operators and apply this study to 1.Verify the Fuglede-Putnam's Theorem, 2.investigate on the orthogonality of the range and the kernel of the generalized derivation induced by some nonnormal classes of operators including posinormal and (p,k)-quasiposinormal operators.