Karyotype analyses of four kinds of hot pepper plants, non-GM control lines of P2377 and P915 and their virus resistant GM events of H15 and B20, respectively, were conducted to confirm the stability of chromosome constitution in transgenic hot pepper plants and to provide a preliminary study for the detection of transgenes on the metaphase chromosomes. Chromosome numbers in somatic cells were 2n=24 in all plants. The karyotypes were composed of ten pairs of metacentrics, one pair of submetacentrics and one pair of subtelocentrics. The length of the mitotic metaphase chromosomes ranged from 3.28 to 4.93 ${mu}m$ in P2377, 3.65 to 5.58 ${mu}m$ in H15, 3.17 to 5.30 ${mu}m$ in P915 and 3.15 to 5.75 ${mu}m$ in B20. Two pairs of secondary constrictions were observed in P2377 and H15, whereas one pair was observed in P915 and B20. Fluorescence in situ hybridization (FISH) revealed that locations of 5S rDNA were at the subterminal parts of the long arms of chromosome d in all plants. Two pairs of 45S rDNA signals were detected on the secondary constrictions in P2377 and H15, whereas one pair of major 45S rDNA signals was detected at the secondary constrictions and one pair of minor signals was detected at the distal parts of chromosome e in P915 and B20. No significant difference in karyotypic constitution was observed between the parental control lines and their transgenic events. The results presented here will be useful in basic studies of breeding and assessment of GM hot peppers.