Technical Abstract: Sixty-four accessions involving five taxa (four species with two taxonomic varieties) of Nephelium were fingerprinted, classified, and evaluated for intraspecific genetic diversity using isozyme polymorphism. All five taxa were polymorphic for most of the ten putative loci encoding eight enzymes. The number of alleles per locus ranged from three for Gpi-1 1to nine for Gpi-2 with a total of fifty-eight alleles. Fifty-five accessions possessed unique fingerprints indicating a significant level of diversity in the collection. On the average, eighty-six percent of the loci were polymorphic and the expected and observed heterozygosities were 0.390 and 0.402, respectively. The cluster analysis of the isozyme data revealed five distinct clusters representing the five taxa included in the study. Isozyme data suggested that the N. hypoleucum is the closest relative of N. lappaceum var. lappaceum. Interestingly, the N. lappaceum var. pallens accessions exhibited closer association with N. ramboutan-ake than with its sibling taxon N. lappaceum var. lappaceum. The isozyme results dispute the taxonomic relationship among the taxa of Nephelium. However, further taxonomic and evolutionary inferences would require a much broader survey on a larger sampling basis.