Chromosomal aneuploidy was a notable cytogenetic character in cancer cells. However, the mechanism of aneuploidy aberration is not clear up to the present. In order to probe into the mechanism of aneuploidy aberration of cancer cells, Centromeric dots (Cd) variation on chromosomes of BGC823 and A549 cells were studied by a simultaneous silver staining of both NOR and Cd from centromeric dots variation. The results showed that: (1) Frequency of Cd loss in BGC823 cells was 1.75%, Cd duplication laggard was 0.28%, small Cd was 1.82%, and Cd-NOR amalgamation was 0.95%. Compared to normal embryonic villi cells, frequencies of Cd loss and Cd-NOR amalgamation of BGC823 cells increased significantly (P<0.0125=, and that frequencies of Cd replication laggard and small Cd showed no difference between BGC823 cells and normal embryonic villi cells. (2) Frequency of Cd loss in A549 cells was 2.73%, Cd duplication laggard was 0.49%, small Cd was 1.73%, and Cd-NOR amalgamation was 0.71%. Frequencies of Cd loss and Cd replication laggard in A549 cells were significantly higher than those of normal embryonic villi cells(P<0.0125), moreover frequencies of Cd-NOR amalgamation and small Cd showed no difference between A549 cells and normal embryonic villi cells. We suggested that Cd loss and Cd-NOR amalgamation might be related with aneuploidy formation of BGC823 cells, and that Cd loss and Cd replication laggard might be related with aneuploidy formation of A549 cells.