Abstract: In view of the vast changes in Cassia taxonomy in recent years, structural analysis of chromosomes and 4C DNA content of 15 species of Cassia has studied to aid in resolving phylogenetic problems. Root tip meristematic cells were pretreated in a aqueous solution of p-Dichlorobenzene and aesculine followed by fixation in Carnoy`s-II solution for chromosome analysis and the method of cytophotometry was followed for the estimation of nuclear DNA content. Somatic chromosome number 2n=28 was observed in all the species except 2n=16 in C. mimosoides, 2n=26 in C. biflora and C. tora, respectively. In addition, aneuploid/polyploid chromosome number plates were also found in most of the species like C. siamea (2n=14, 28, 35), C. biflora (2n=24, 26), C. mimosoides (2n=16, 30), C. fistula (2n=24, 28), C. tora (2n=28, 52). Minute details of the karyotype showed structural alteration of chromosomes in spite of the same diploid chromosome numbers in some species. In C. mimosoides the size of the chromosomes was quite large (2.06-3.34 μm); significant variations in the chromosome length were observed among different species from 31.48 μm in C. roxburghii to 57.48 μm in C. tora. Total chromosome volume also varied significantly among the studied species from 12.38 μm3 in C. renigera to 24.02 μm3 in C. occidentalis. Highest centromeric index percentage (45.96%) was noted in C. grandis and that of lowest (36.09%) in C. mimosoides. Significant variation in 4C nuclear DNA content was noted among the species that varied from 7.59 pg in C. absus to 35.63 pg in C. siamea. The correlation coefficients shows the various chromosomal and nuclear parameters are interdependent to some extent suggesting a interspecific relationship between structural and genetic changes of the genome architecture during evolution of speciation.