  We consider instanton effects in a non-supersymmetric gauge theory obtained
by marginal deformations of the N=4 SYM. This gauge theory is expected to be
dual to type IIB string theory on the AdS_5 times deformed-S^5 background. From
an instanton calculation in the deformed gauge theory we extract the prediction
for the dilaton-axion field \tau in dual string theory. In the limit of small
deformations where the supergravity regime is valid, our instanton result
reproduces the expression for \tau of the supergravity solution found by
Frolov.
