Hybrids between the great sturgeon and the Russian sturgeon in reciprocal crosses are found to exhibit non-intermediete chromosome number, 2n=167-169, on average. The hybrids are also characterized by sharp increase in variability of the quantitative karyotypic parameters such as diploid chromosome number, bi-armed chromosome number, number of uni-armed and microchromosomes, and chromosome arm number. Measurements of erythrocytes and their nuclei confirmed the di-tetraploid relationship of the parental species and non-intermediate pattern of the hybrid genome. Sharp disbalancing of karyotype of both reciprocal hybrids is indicative of high probability of their complete sterility.