Flooding and submergence are major abiotic stresses and are serious problems for growth and yield of flood sensitive crop. Excessive generation of reactive oxygen species (ROS) under oxidative stress is an integral part of the many stress situations including oxygen shortage. Generation of ROS is the characteristics for hypoxia and re-oxygenation. Protection against ROS involves several antioxidants and most important pathway is ascorbate- glutathione cycle. Ascorbate peroxidase catalyzes the first reaction and is consider being a key rate limiting enzyme of this pathway. This book describes the possible role of Ascorbate peroxidase and its regeneration system with flooding tolerance mechanism in rice. This may help to propose new strategies to analyze APX gene knockout or to engineer transgenic plant (i.e. rice) tolerance to flooding stress. This book should especially useful to researchers / scientists in agriculture and life science field for future development of flooding tolerant rice cultivars.