Abstract: Metaphase chromosome specimens of Polyodon spathula,injected with PHA and colchicin,were prepared from short-term culture of kidney cells with air-drying technique.It diploid chromosome number was 2n=120.The karyotype was composed of 44m,32sm and 44st,t chromosomes,NF=196.Diploid nucleus DNA content was measured from the somatic cell of P.spathula,using flow cytometer(Beckman cell Lab Quant,made in USA) and the DNA content(2.3pg/N) of erythrocytes of chicken(Gallus domestica) as standard.The DNA content of P.spathula was 6.18pg/N,which was corresponded with the result measured chromosome number as ploidy.According to the present results and date reported,P.spathula was possibly a tetraploid(4n).Combination of the present results and data reported among Acipenseriformes including two families and six genera,Acipenseriformes was the polyploid origin's fish,and was quite completely special at the cell level which evolved by chromosome doubling.The chromosome's doubling and differentiation possibly were primary caused of polyploidization and polyploid type(4n,8n,12n and so on) richly.Polyoidization had played an important role in the diversity of Acipenseriformes.