Streptococcus agalactiae (Group B Streptococcus; GBS) is an important pathogen and is associated with pneumonia, sepsis and meningitis in neonates and adults. GBS infections induce cytotoxicity of respiratory epithelial cells (A549) with generation of reactive oxygen species (ROS) and loss of mitochondrial membrane potential (ψm). The apoptosis of A549 cells by GBS was dependent on the activation of caspase-3 and caspase-9 with increased pro-apoptotic Bim and Bax molecules and decreased Bcl-2 pro-survival protein. Treatment of infected A549 cells with ROS inhibitors (diphenyleniodonium chloride or apocynin) prevented intracellular ROS production and apoptosis. Consequently, oxidative stress is included among the cellular events leading to apoptosis during GBS human invasive infections.