The intensive study of physical properties and growth process of ZnO crystals is caused by its unique electrical and optical properties. Zinc oxide crystals can be considered as an alternative to gallium nitride for use in optoelectronic devices. In the present work ZnO crystals were grown by Chemical Vapour Transport (CVT). During growth, partial pressure of zinc vapour was varied. The high-resolution diffraction study was performed in triple-axis mode using an X'Pert MPD diffractometer. The studied crystal had natural (110) and (001) external faces. Lattice parameters were determined from 110 symmetric and 112 asymmetric reflections. The changes of the colour observed in the crystal suggest that the Zn:O ratio varies along the crystal. It is necessary to admit, that the change of colour was not related to the change of crystallographic orientation. The parts of the crystal exhibiting different colours are found to have distinct c lattice-parameter values , whereas the a parameter is virtually the same in all parts of the crystal. The determined lattice parameters are different then the standard JCPDS. These deviations from standard parameters can be explained by the different oxygen concentration at different crystal parts. In the present work, the structural characteristics of bulk zinc oxide crystals, and their dependences on CVT growth process were done in details. The work was supported by the Ministry of Education and Science of Poland under the grant Nr.3T08A05128.