The promotion of the photocatalytic activity of the Cd0.3Zn0.7S nanoparticles via deposition of some copper species, such as CuxS and Cu0, as a co-catalyst, in the hydrogen production under visible light irradiation from aqueous solutions of a sacrificial Na2S/Na2SO3 system was studied. The state of the samples was characterized with a wide range of physical methods both in the initial state as well as after their photocatalytic operation. An evolution of both photocatalytic activity and the state of the photocatalyst particles was registered by a set of the physical methods. The highest apparent quantum efficiency and photocatalytic activity which were achieved at illumination by light with λ = 450 nm over the 0.1 wt% CuxS/Cd0.3Zn0.7S sample for the photocatalytic hydrogen evolution from Na2S/Na2SO3 aqueous solutions were 23.1% and 6.4 mmol g−1 h−1, respectively. It was shown that the deposited Cu species undergo the transformation to CuxS during the photocatalytic production of hydrogen, and these are the copper sulfide nanoparticles that increase the activity of the Cd1-xZnxS solid solutions. This statement agrees well with the principle of a constancy of the state of heterogeneous catalysts under their operation in the same reaction media established by G.K. Boreskov in the 1950s.