  In this paper, we argue that one can calculate the weak deflection angle of
light in the background of Einstein-Maxwell-Dilaton-Axion black hole using the
Gauss-Bonnet theorem. To support this, the optical geometry of the black hole
with the Gibbons-Werner method are used to obtain the deflection angle of light
in the weak field limits. Moreover, we investigate the effect of a plasma
medium on deflection of light for a given black hole. Because of dilaton and
axion are one of the candidate of the dark matter, it can give us a hint on
observation of dark matter which is supported by the black hole. Hence we
demonstrate the observational viability via showing the effect of the dark
matter on the weak deflection angle of light.
