  We present a procedure for application of T-duality transformation on
scattering amplitudes of closed bosonic stringy states. These states arise due
to compactification of closed string to lower spacetime dimensions through
dimensional reduction. The amplitude, in the first quantized formalism, is
computed by introducing vertex operators. The amplitude is constructed by the
standard prescription and the vertex operators are required to respect
conformal invariance. Such vertex operators are constructed in the weak field
approximation. Therefore, the vertex operators of the stringy states of our
interest are to be defined accordingly. We propose a prescription to implement
T-duality on the three point functions and N-point functions. We argue that it
is possible to generate new amplitudes through the transformations on a given
amplitude just as T-duality transformations can take us to a new set of string
vacuum when acted upon an initial set. Explicit examples are given for three
point and four point functions.
