Abstract. Donbundit N, Bausriyod P, Tanomtong A, Srisamoot N, Sumontha M, Thongnetr W, Patawang I, Supiwong W, Ditcharoen S, Muanglen N, Kaewmad P. 2022. Karyomorphological delineation, and the NOR loci on the sex chromosome in three species of Chrysopeleinid (Chrysopeleinae: Colubridae) from Thailand. Biodiversitas 23: 3813-3819. The description of chromosomal characteristics of three snakes from Thailand namely, Ahaetulla fusca, A. prasina, and Chrysopelea ornata was by using conventional staining and Ag-NOR banding techniques. The results showed that the same diploid chromosome number (2n) = 36 (16 macrochromosomes + 20 microchromosomes) and the fundamental number (NF) was 54 while the karyotype formulae in these three species are as follows: A. fusca; 2n(36) = Lm6 + Sm2+ Ssm4 + Sa2+ ZZ/ZW + 20 microchromosomes, A. prasina; 2n(36) = Lm6+ Sm6+ Sa2+ ZZ/ZW + 20 microchromosomes and C. ornata; 2n(36) = Lm4+ Lsm2+ Sm2 + Ssm4+ Sa2+ ZZ/ZW + 20 microchromosomes. Besides, the ZZ/ZW sex chromosome was observed in all species, whereas C. ornata was discovered the heteromorphic sex chromosome for the first time. Nucleolar organizer regions (NORs) are located on telomeric region of one pair in all species, while located on microchromosomes in A. fusca and A. prasina, whereas C. ornata was detected on sex chromosomes. Therefore, the Z chromosome revealed the NOR on the telomeric region of the long arm, while NOR of the W chromosome was located on the telomeric region of the short arm.