Samples of graphite electrochemically intercalated with FeCl4- in CH3NO2 solution are studied by scanning tunneling microscopy (STM) from a submicrometer to atomic scale. A new long range triangular modulation of the charge density is observed on the surface. This modulation is superimposed on the usual graphite periodicity. This new structure is tentatively attributed to a charge density wave (CDW) resulting from the charge transfer between the intercalated species and the graphite host.