Study was conducted for cytogenetic analysis of S U.99 cell line, for 6 successive passage in tissue culture. Results were compared with normal cytogenetic analysis of 15 normal female BALB/c mouse of spleen cells classified into of 3 groups. Cell showed variation in chromosome number of diploid (2n), tri ploid (3n), tetra-ploid C(4n), pentaploid (5n), hexaploid (6n), heptaploid (7n) and octoploid (8n), also this study showed variation in chromosomal structur as metacentric chromosome (MC), minute and double fragment (MF) (DM), ring chromosome (RIC), stickines's chromosome (STC), chromatid break (CB) that have been demonstrated in different percentage. Cytogenetic analysis of cells of secondaiy tumour prepared from tumour biopsy of S.U.99 cell line induced tumour in BALB/c mice gave the same morphological picture of the original cell. An inormous increase in the number chromosomes eight times the normal chromosomal number such as (7n) heptaploid and (8n) octoploid and chromosomal structural changes such as metacentric mhromosome (MC) and double minutes (DM)s, were similar to the previously identified in the original S.U.99 cells.