The entire National Park area is covered by mangrove forest. There are small patches of brackish marshes on emerging islands and riverbanks, and sandy areas with grass and low shrubs on some of the outer islands. The two dominant mangroves are Sundori (Heritiera fomes) and Gewa (Excoecaria agallocha).

Sundarbans is home to many different species of birds, mammals, insects, reptiles and fishes. Over 120 species of fish and over 270 species of birds have been recorded in the Sundarbans. The Gangetic River Dolphin (Platanista gangeticus) is common in the rivers. No less than 50 species of reptiles and eight species of amphibians are known to occur. The Sundarbans now support the only population of the Estuarine, or Salt-Water Crocodile (Crocodylus parasus) in Bangladesh, and that population is estimated at less than two hundred individuals.

About 32 species of mammal are still found in this forest. Among these are Rhesus Macaques, Clawless Otters, Leopard Cats, Fishing Cats and Spotted Deer. The entire Sundarbans Forest comprises the largest remaining tract of habitat for the Royal Bengal Tiger (Panthera tigris).