In the paper changes of neutron reflectivity of big (120 x 70 x 10 mm(3)) Cu single crystalline monochromators and CoFe (8 %at.) single crystalline, polarising monochromators after cold hammering of the starting plates, are described. An almost three times higher number of reflected neutrons (total reflectivity) and about 20 % higher intensity in peak maximum were observed, for Cu plates (measured in reflection from (220) plane)), while the mosaic's spread was about 2 times higher than the one measured for a non-treated plate. In the case of CoFe, 3 mm thick plates, a two times higher number of reflected neutrons and almost 60 % higher intensity in peak maximum were observed (measured in transmission - from (200) plane) after hammering, while the mosaic's spread increase was rather small (about 15 %).