In spite of previously reported stannite type structure for CZTSe, CZTS and CZTSe crystallize both in the kesterite type structure (space group ) [1,2] which can be derived from the cubic sphalerite type structure by doubling the unit cell in the direction of the crystallographic c-axis and ordering of the cations. In the literature only X-ray diffraction was used for structural characterization of CZTSSe solid solution [3]. A differentiation between the isoelectronic cations Cu⁺ and Zn²⁺ and consequently kesterite and stannite type structures is not possible using X-ray diffraction due to their similar scattering factors. But neutrons diffraction can solve this problem; the coherent scattering lengths are sufficiently different for these cations. It was shown by this method that both Cu₂ZnSnS₄ and Cu₂ZnSnSe₄ occur in the kesterite structure [4].  A detailed structural analysis of Cu₂ZnSn(S_1-xSe_x)₄ powder samples with x= 0.48, 0.58, 0.70, 0.79, 0.90, 1, grown by solid state reaction, was performed by neutron diffraction. Rietveld refinement of neutron diffraction data using the FullProf suite software [5] lead to accurate values of lattice constants and site occupancy factors. From the latter the average neutron scattering length was derived which has given insights into the cation distribution within the crystal structure of Cu₂ZnSn(S_1-xSe_x)₄ solid solution with different x values.