  The tree-level amplitudes in $\beta$-deformed theory are studied from twistor
string theory. We first show that a simple generalization of the proposal in
hep-th/0410122 gives the correct results for all of the tree-level amplitudes
to the first order of the deformation parameter $\beta$. Then we give a
proposal to all orders of $\beta$ and show this matches the field theory. We
also show the prescription using connected instantons and the prescription
using disconnected instantons are equivalent in the deformed twistor string
theory. The tree-level amplitudes in non-supersymmetric $\gamma$-deformed
theory are also obtained in this framework. The tree-level purely gluonic
amplitudes in theories with generic marginal deformations are also discussed in
the twistor string theory side.
