Bangladesh, a country that lies on the north shores of the Bay of Bengal, has been blessed with a plethora of natural resources. St. Martin’s Island, the only coral-bearing island in Bangladesh, is undoubtedly regarded as one of the most prized possessions. It is rich in biodiversity, but truly scientific information on it is lacking. In the present investigation, 14 stations adjacent to St. Martin’s Island within the Bay of Bengal were sampled for determining the composition, spatial distribution, species richness, and diversity of pelagic zooplankton. Samples were collected in the pre-monsoon hot season. From the community of zooplankton, 34 species were reported. Most of the species belonged to copepods. Besides, Polychaeta and Cirripedia were also present in the community. The most significant species belonged to Oithona, Canthocalanus, Balanus, Euterpina, and Microsetella. Total zooplankton standing crop varied from 45,000–125,000 ind/m3 and the highest number of species (8) were observed at station 7. Strong variability in the distribution of species was observed in the studied stations. The number of genera collected at each station varied from 4–8. Data on species richness (Df) varied from 1.30–3.04 and that of the Shannon-Wiener Index (H) from 1.33–1.93. The species composition of zooplankton and the species richness and the diversity index of the population was comparable to the other studies carried out in the Central and Western Bay of Bengal.