Double and triple X-ray diffractomery was used for a structural characterization of the short-period superlattices (SLs) CdSe/ZnSe with submonolayer sheets of CdSe. The multilayer structures containing SLs were grown by molecular beam epitaxy (MBE) on (001) GaAs substrates. The period of SLs was in range (30-60 A), the nominal thickness of CdSe sheets varied from 0.2 to 1.2 monolayer. The parameters of SLs have been determined. Broadening of CdSe sheets in direction normal to interface has been revealed. Full width at half maximum (FWHM) of this broadening is equal to about 4.5 monolayers and does not depend on the period and content of Cd in SLs.