We study the behaviour of surface waves propagating along the ionopause of the planet Mars and derive the onset criteria for unstable Kelvin Helmholtz modes and negative energy waves at the Martian ionopause. Growth rate of unstable Kelvin Helmholtz mode decreases with wavelength. The backward propagating waves became negative energy waves for the ionosheath velocity higher than critical velocity. It is found that short wavelength surface waves propagating along the Martian ionopause are less dispersive than long waves.