In this work we have investigated the relation between the observed decay of reflection high energy electron diffraction intensity oscillations and critical layer thickness in case of strained InxCa1-xAs/GaAs structures. The Value of decay time constant of oscillations depends on growth parameters and on lattice mismatch, too. Remarkable correspondences were found between the value of mismatch and the decay time constant. The critical layer thickness determined in this way is in good agreement with other results known from the literature.