Abstract: The regulatory effect of exogenous γaminobutyric acid (GABA) on metabolism of reactive oxygen species (ROS) in melon chloroplasts under shortterm salinityalkalinity stress were investigated in melon variety ‘Jinhui No.1’, which was cultured with deep flow hydroponics. The result showed that under salinityalkalinity stress, the photosynthetic pigment content, MDA content, superoxide anion (O^-_·2) production rate and hydrogen peroxide (H₂O₂) content in chloroplast increased significantly, the contents of antioxidants ascorbic acid (AsA) and glutathione (GSH) increased, and the activities of H⁺-ATPase and H⁺-PPiase were inhibited obviously. With exogenous GABA application, the accumulations of O^-_·2, MDA and H₂O₂ induced by salinityalkalinity stress were inhibited. Exogenous GABA alleviated the increase of photosynthetic pigment content, improved the activity of SOD, enzymes of AsAGSH cycle, total AsA and total GSH while decreased the AsA/DHA ratio and GSH/GSSH ratio. Foliar GABA could enhance the H⁺-ATPase and H⁺-PPiase activities. Our results suggested that the exogenous GABA could accelerate the ROS metabolism in chloroplast, promote the recycle of AsA-GSH, and maintain the permeability of cell membrane to improve the ability of melon chloroplast against salinityalkalinity stress.