The Acinetobacter sp. VITRSA1 strain was isolated from the Pichavaram (mangrove), Tamil Nadu, India; and confirmed as gram-negative, aerobic, and non-motile bacteria. The 16S rRNA gene sequence analysis showed 99% similarity with Acinetobacter calcoaceticus JO1 and the Antibiotic Susceptibility Test (AST) showed; resistant to ampicillin, bacitracin, and trimethoprim; intermediate resistant to methicillin, and sensitive to streptomycin. The Acinetobacter sp. VITRSA1 strain was able to form biofilm at 25 °C and 37 °C, on Congo-Red agar plate with a metallic sheen and also on SLI (solid-liquid interface) and ALI (air-liquid interface) – confirmed using microtitre plate, and coverslip assays, respectively. The biofilm formation on Paratelphusa hydrodromous (freshwater crab) showed strong adhesion of bacteria to the crab shell and produced lesions, eventually causing mortality to crabs - indicating shell disease. On contrary to the pathogenicity, the Acinetobacter sp. VITRSA1 was able to degrade toluene and use it as a sole carbon source, which can be useful in recycling industries. This study demonstrates the biofilm formation and antibiotic resistance property of newly isolated Acinetobacter sp., from the mangrove ecosystem and its ability to cause mortality among crabs along with its bioremediation potentials. © 2020