Abstract: This is the first paper to report the observations of the karyotype and banding patterns of the cell of ascites reticulum-cell sarcoma (ARS) in mouse,which has been established in our country.ARS is a hyperdiploid tumor.Modal number of the chromosomes is 44 (37.7%).Seven marker chromosomes were discovered.Morphological characteristics,the distributions of G- and C-bands and the location of nucleolus organizer regions (NORs) of the tumor chromosomes were described in detail.