Objective To explore the survival/proliferation, apoptotic and death effects of keratinocyte growth factor (KGF) in alveolar epithelial type Ⅱ cells (ATⅡCs) exposed to hyperoxia. Methods Primary culture of ATⅡCs from the Sprague-Dawley rat fetuses was studied under room air condition (210 mL/L O2) and hyperoxic condition (950 mL/L O2) for 0.5-12.0 h. Various concentrations of KGF (15 μg/L, 25 μg/L, 50 μg/L, 75 μg/L, 100 μg/L) were added into the cell cultures.Cells were randomly divided into room-air group, room-air-KGF group, hyperoxic-exposure group and hyperoxic-exposure-KGF group.The levels of intracellular reactive oxygen species(ROS), cleaved cysteinyl aspartate specific proteinase-3 (Caspase-3), cell death and proliferation of ATⅡCs were measured by flow cytometer, Western Blot, release of lactate dehydrogenase assays (LDH assays) and 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assays (MTT assays), respectively. Results Under room air condition, KGF could significantly increase ATⅡCs proliferation with 15-100 μg/L in a dose-dependent manner and significantly decrease LDH production at concentrations of 25-100 μg/L.Exposure to hyperoxia resulted in a significant increase in intracellular ROS production in ATⅡCs in a time-dependent manner compared with that of the room air group.Cell viability decreased and LDH release increased significantly in a time-dependent manner when ATⅡCs were exposed to 950 mL/L O2 for more than 4 h. After exposure to hyperoxia for 0.5 h and 1 h, KGF could significantly increase ATⅡCs proliferation in 15-75 μg/L and significantly decrease LDH production at concentrations of 25-75 μg/L.After exposure to hyperoxia up to 4 h, higher viability was observed in 15 μg/L and 25 μg/L KGF group, and lower death rate presented in 25-100 μg/L KGF group.Further, prolonged hyperoxic exposure for 8 h, high viability was shown only in 50 μg/L KGF group, and less death rate was observed only in 75 μg/L KGF group.In addition, no significant difference in viability and mortality was found between hyperoxic group and hyperoxic-KGF group after hyperoxic exposure for 12 h. Expression of cleaved Caspase-3 was significant higher after 4 h and 8 h hyperoxic exposure than that in room-air group; at the same time, by adding 25 μg/L and 75 μg/L KGF led to decreased expression of Caspase-3 was detected, compared to hyperoxic group. Conclusions KGF may promote survival/proliferation, inhibited apoptosis and death of rat fetal ATⅡCs in room air condition or under temporary exposure to hyperoxia in vitro.However, prolonged exposure to hyperoxia may decrease the sensitivity of AECⅡCs to KGF and limit its protective effects on lung injury. Key words: Hyperoxia-induced lung injury; Oxidative stress; Keratinocyte growth factor; Alveolar epithelial type Ⅱ cells