Abstract: The meiosis of pollen mother cells was observed and karyotype analysis of root tip cells was carried out respectively in F₁ and F₂ hybrid progeny of N. tabacum Hicks and medicinal plant Coimum bailicm L.The results indicated that chromosome number of interfamily hybrid progeny was unfixed and aneuploid, the euploid and aneuploid coexisted in one plant.Viewing from chromosome morphology of pollen mother cells, there presented some abnormal multivalent chromosomes in the shapes of "8", "0" and some univalent chromosomes.The karyotype of a group of root tip cells (2n=38) was analyzed and it was found that the sixth pair of chromosomes was trisomic;a univalent chromosome with one satellite was also found, its karyotype and karyotype formula were 2B and 2n=38=26m+8sm+1Ш+1Ι, respectively.