Abstract. An element a of a semigroup S is called left [right] magnifying if there exists a proper subset M of S such that S = aM [S = M a]. Let X be a nonempty set and T (X) be the semigroup of all transformations from X into itself under the composition of functions. For a partition P = {X α | α ∈ I} of the set X, let T (X, P ) = {f ∈ T (X) | (X α )f ⊆ X α for all α ∈ I}. Then T (X, P ) is a subsemigroup of T (X) and if P = {X}, T (X, P ) = T (X). Our aim in this paper is to give necessary and sufficient conditions for elements in T (X, P ) to be left or right magnifying. Moreover, we apply those conditions to give necessary and sufficient conditions for elements in some generalized linear transformation semigroups.