This study investigates the acute toxicity of sublethal tributyltin (TBT) exposure in the marine polychaetes Perinereis aibuhitensis by measuring changes in mortality, burrowing activity, acetylcholinesterase (AChE) function, and antioxidant defense mechanisms. The 96h-LC50 of TBT was established at 23.7 μg L⁻¹. Following exposure to 1 μg L⁻¹ of TBT led to a dose-dependent reduction in burrowing behavior and AChE activity in polychaetes. Elevated levels of malondialdehyde (MDA) and pronounced reduction of glutathione (GSH) contents explained significant oxidative stress. The major antioxidant enzymes, including GSH peroxidase, GSH reductase, catalase, and superoxide dismutase, were also significantly suppressed following TBT exposure. These findings indicate that TBT-induced acute toxicity compromises physiological functions and undermines antioxidant defense system in polychates.