Coral reefs ecosystems are some of the most productive and diverse in the world. The symbiotic association between cnidarians and their symbiotic microalgae is of great importance in coral reef ecosystems; however, its underlying molecular mechanism remains unclear even after decades of research. Rab small GTP binding proteins are critical regulators of vesicle trafficking. Here we present the experimental evidence supporting a possible association of ApRab37 with the surface of lipid droplets in the endosymbiosis between the sea anemone, Aiptasia pulchella and the symbiotic dinoflagellate (commonly known as zooxanthellae). ApRab37, a protein of 215 amino acids, displays strong homology with human Rab37. In transfected COS7 cells, EGFP-ApRab37 localized to lipid droplets and clustered in the peri-nuclear region, which stained positive for the ER (endoplasmic reticulum) marker. Immunostaining analysis found ApRab37 associated with symbiosomes and lipid droplets, which was also confirmed by Western blot analysis of in the enrich lipid droplet fraction. Phagocytosis assay showed that ApRab37 involved in late phase of phagocytosis. DCMU treatment indicates symbiosome association of ApRab37 is mediated by zooxanthellae. I propose that ApRab37 plays a pivotal role in the regulation of lipid trafficking from the symbiosomes to the host cell during the Aiptasia-zooxanthellal endosymbiosis.