The insertion reaction of Li and Na in lamellar InSe single crystal was performed electrochemically in a non-aqueous electrolyte at room temperature. The insertion product was, at the electrode surface, an intercalation compound (LixInSe, NaxInSe) or the result of the chemical decomposition of the electrode material (Li2Se, Na2Se). The development of the reaction was followed by photoelectrochemical spectroscopy and by cyclic photocurrent voltammetry performed in situ in the reaction electrolyte. A Fermi level shift in the intercalation compound was deduced by a flatband shift to lower potential and a small increase of the bandgap energy resulted from the intercalation reaction. The Na-inserted samples have been analyzed by grazing angle incidence X-ray diffraction and an increase in the interlayer distance was observed.