Abstract: Gibel carp (Carassius auratus gibelio), a unique polyploid fish, is discovered to be able to reproduce by gynogenesis or sexuality reproduction. Since the allotetraploid gibel carp with 212 chromosomes were discovered from the gynogenetic offspring of gibel carp activated by red common carp sperm in 1990s, a lot of works have be done to study the genome organization and formation mechanism of them. The observations of genomic in situ hybridization and 45S rRNA gene localization on the allopolyploid metaphases showed the unusual allotetraploid gibel carp which contain the whole chromosomes of gibel carp and one chromosome set of common carp. However, the histological characterizations of allotetraploid gibel carp still remain unknown. In this study, we compared the histological features and found significant differences in peripheral blood cells and testis tissues between triploid (D clone) and allotetraploid gibel carp. The HE staining results showed that there were many abnormal red blood cells with small, round nuclear in the blood cell smear of allotetraploid gibel carp, which was obviously different from red blood cells with oval-shaped nuclear of triploid gibel carp. Moreover, the dual-nuclear red blood cells indicated a trend of cell division in peripheral blood of the allotetraploid gibel carp. Meanwhile, using the flow cytometry technique, we compared the DNA histogram of peripheral blood cells between triploid and allotetraploid gibel carp. The result revealed the existence of two kinds of cells with different DNA content in peripheral blood of allotetraploid gibel carp. In addition, we observed three testis types of allotetraploid gibel carp: TypeⅠ, wild type, which the sperm development was as normal as that of the male D clone gibel carp and large quantity of spermatids and sperms could be found in spermatogenic cysts; TypeⅡ, in which spermatids and sperms could not be observed in spermatogenic cysts; and Type Ⅲ, lacking the structure of spermatogenic cysts. Among those three types, TypeⅡ and type Ⅲ were the mainly forms of testis in allotetraploid gibel carp. To further study the characterizations of sperm development, fluorescent immunostaining was performed to compare different testis types of allotetraploid gibel carp by using the vasa antibody. The result revealed that germ cells in TypeⅠtestis could complete the meiosis process and produce a large number of spermatids and sperms in breeding season, while TypeⅡ testis was observed considerable quantities of primary and secondary speratocytes without spermatids in its spermatogenic cysts, indicating that germ cells cannot complete the second meiosis process in TypeⅡ testis. The unique characterization of red blood cell and testis could broaden our understanding about allotetraploid gibel carp.