Abstract. Basith A, Abinawanto, Kusrini E, Yasman. 2021. Genetic diversity analysis and phylogenetic reconstruction of groupers Epinephelus spp. from Madura Island, Indonesia based on partial sequence of CO1 gene. Biodiversitas 22: 4282-4290. Groupers populations in Indonesia, particularly from Madura Island, East Java are indicated to be over-fished, thereby requiring data collection of more accurate genetic resources as an important step for grouper conservation. A total of 14 samples of the Epinepheplus groupers were obtained from the fish landing port on Madura Island. The 617 bp CO1 gene sequence was utilized for genetic diversity analysis and phylogenetic tree reconstruction. Genetic diversity is based on the value of haplotype diversity (Hd) and nucleotide diversity (?). Reconstruction of the phylogenetic tree includes neighbor-joining (NJ) implementing K2P substitution model, while maximum likelihood (ML) is conducted by implementing HKY+G+I substitution model, both of which were evaluated by employing a bootstrap of 1000 replications. Analysis of genetic distance between species indicated that the farthest distance between E. heniochus and E. fasciatus was 0.189, while the closest distance between E. erythrurus and E. ongus was 0.099. Intrapopulation genetic diversity indicated a high value with details of Hd=0.978 and ?=0.12107. Furthermore, NJ and ML phylogenetic tree demonstrated similar topology in the observed Epinephelus spp. obtained from Madura Island grouped into 7 clades, that is Epinephelus coioides, E. bleekeri, E. areolatus, E. erythrurus, E. heniochus, E. fasciatus, and E. ongus.