Abstract: The mitosis and meiosis of Pseudoxenodon macrops had been investigated,using conventional Giemsa and silver staining and BrdU induced condensation inhibition.The diploid number is 2n=36 with 16 macro- and 20 microchromosomes (macro autosomes are 10 metacentric and 6 submetacentric).Silver staining NORs were localized on the microchromosomes pair No.1.The high resoluting banding of Pseudoxenodon macrops is sucessfully made by blocking the cycle of cell with large dosage of TdR and incoporating BrdU into the replicating chromosomal DNA during synthesis phase.These banding patterns allow for the first time a precise identification of all macro-chromosomes and the analysis of the patterns of replication in the various stages of S-phase in snake.This information could clarify the taxonomic and phylogenetic relationships among certain familes of colubrinae as well as the evolutionary relationships within certain families.