Koi fish (Cyprinus carpio Linn.) is an ornamental fish with high economic value and has long been cultured in Indonesia. Koi fish has a uniqueness appeared from its phenotype and wide intraspecies genetic variation. Genetic analysis i.e. cytogenetics is important to gain information about species relatedness, chromosomal abnormalities, and further lead to the fish culture development. Koi fish chromosome information in Indonesia has not been reported so far. Therefore the aim of this study was to obtain information about the chromosomes of Kohaku koi fish in Indonesia. In addition, in this study, we applied CHIAS (Chromosome Image Analyzing System) software to study koi fish chromosome karyotyping for the first time. The cells were cultured using Roswell Park Memorial Institute medium at a temperature of 37 °C in a 5 % CO2 incubator. The cell synchronization at metaphase was carried out by two-hours colcemid treatment. The samples were then subjected to a hypotonic solution and fixed with a solution of methanol and glacial acetic acid. According to the results, koi fish chromosome number ranged from 2n = 100 to 2n = 102. Furthermore, koi fish chromosomes could successfully be arranged based on their size by using CHIAS. In conclusion, koi fish chromosome numbers were varied and CHIAS has been proven to be powerful to analyze the small size and the high number of chromosome. Results of our study could further be applied for other koi chromosome researches as well as for the development of cytogenetics in Indonesia.