Mehdi Jafari - Department of Mathematics, Payame Noor University, PO BOX ۱۹۳۹۵-۴۶۹۷, Tehran, Iran.
Razie Darvazebanzade - Department of Mathematics, Payame Noor University, PO BOX ۱۹۳۹۵-۴۶۹۷, Tehran, Iran.

In this paper, we apply the approximate symmetry transformation group to obtain the approximate symmetry group of the perturbed mKdV-KS equation which is a modified Korteweg-de Vries (mKdV) equation with a higher singularity perturbed term as the Kuramoto-Sivashinsky (KS) equation. Also, an optimal system of one-dimensional subalgebras of symmetry algebra is constructed and the corresponding differential invariants and some approximately invariant solutions of the equation are computed.

Perturbed mKdV-KS equation, Approximate symmetry, Approximately invariant solution, Optimal system