Scleropages formosus is an important aquarium fish with high economic value. In order to explore its cytogenetic background, the metaphase chromosomes were observed. The phytohemagglutinin (PHA) and colchicine were injected in vivo,and kidney cells were collected and treated with low osmotic solution, and finally chromosome spread was prepared by air-drying technique. The karyotype was analyzed. The results showed that S. formosus had a diploid chromosome number of 50 and the karyotype formula was 2n=2m+8sm+8st+32t, NF=60. These data will be helpful for understanding the idioplasm and systematic evolution of S. formosus.