In the context of the global H2O cycle, an active interest is taken in water recycling associated with subduction of oceanic plates into the mantle. Mineral serpentine, Mg3Si2O5(OH)4, is regarded as the main water reservoir in oceanic litosphere , and therefore its dehydration can produce a large impact onto seismic activity and magma generation in subduction zones. Since the dehydration temperature can be effectively decreased in the presence of alkali chlorides , we explore this effect on serpentine dehydration. Here we report the results of in-situ X-ray diffraction and Raman spectroscopy studies of two serpentine minerals, chrysotile and antigorite, in the presence of sodium chloride at high P-T conditions relevant to subduction zone (1-4 GPa, 400-800oC). The dehydration temperature of both minerals is about 200 degrees lower compared to salt-free H2O-saturated conditions, which is important for the localization of dehydration reactions in subducting slab. This work is supported by the Russian Foundation for Basic Research (grant No 18-05-00312). Diffraction experiments were performed at SSTRC, Novosibirsk (project RFMEFI62119X0022) and the PETRA III (DESY, Hamburg), and supported by approval of PETRA III Proposal I-20190140.