Calcifying marine organisms respond critically to decreased CaCO₃ saturation due to ocean acidification and metal accumulation, slowing growth and calcification. This study evaluated the effects on the shell structure of the bivalve Crassostrea brasiliana under multiple stressors: marine acidification and sediment Pb contamination. The experiment exposed the organisms to three pHs (8.0, 7.6, 7.2) and Pb (30 and 210 mg/L). After exposure, shell strength was measured using a mechanical press. The results showed that strength was affected by both pH and Pb, with the effects of metal being more critical under predicted acidification scenarios.