This study aimed to investigate abnormal chromosomal behaviour in mitosis resulted from Ethyle methane sulphonate ( EMS ) and Endoxan . Commercial onion bulbs were used as a material of  mitotic  cell division  . In addition , this study compared  between the effect of mutagenic agent ( EMS ) with anticancer compound  (Endoxan ) on mitotic index  . Onion bulbs were germinated under the effect of EMS and Endoxan , in addition to control treated with  tap water . The differences between treatments and  control were statistically evaluated . The results achieved that mitotic index of control had the largest number of normally divided cells  about 15% , while Endoxan  about 10% and EMS about 4% . This indicated  that EMS had a strong effect of inhibiting mitosis than of Endoxan.    In general , Endoxan and EMS reduced mitotic index than control  in addition to several types of chromosomal aberrations . These chemical agents included sticky chromosomes , anaphase bridge chromosomes , lagging chromosomes , disrupted chromosome segregation  and star cluster  chromosomes . with variable percentage of each type. This reflects the dangerous of these chemical compounds on mitotic cell division .