In this paper,the genome size (C-value) and ploidy of 5 commercial fishes including Onychostoma sima,triploid Cyprinus carpio var. singuonensis,Myxocyprinus asiaticus,Sinibotia superciliarisa and Hemibarbus maculatus were determined by flow cytometry using chicken erythrocyte DNA content as a standard. The results showed that the C-values of O. sima,triploid C. carpio var. singuonensis,M. asiaticus,S. superciliarisa and H. maculatus were 1.18±0.01 pg,1.92±0.07 pg,2.62±0.28 pg,0.89±0.01 pg and 1.24±0.02 pg,respectively. The C-value of M. asiaticus was the largest,followed by triploid C. carpio var. singuonensis, H. maculatus,O. sima and S. superciliarisa. Among the 5 economic fishes,there is no difference in C-values between O. sima and H. maculatus (the same family) (P＞0.05),but the difference between the other species (different families) was significant (P<0.05). Ploidy analysis showed that O. sima,S. superciliarisa and H.maculatus were diploid,C. carpio var. singuonensis was triploid and M. asiaticus was tetraploid.