In this study, the effect of high concentrated dissolved oxygen on the lettuce plant growth in a deep hydroponic culture under a low greenhouse temperature has been investigated. The nutrient solution containing 20-30 mg/l dissolved oxygen was made using an Oxygen Enricher. From the Henry's law, the solubility of oxygen in the air mainly depends on water temperature and the partial pressure of oxygen in the air. This high concentrated dissolved oxygen is made by passing the nutrient solution in the high-pressure pure oxygen gas (95% O2). The study aimed to improve lettuces plant growth grown in hydroponic under a low temperature condition by applying the high concentrated dissolved oxygen to the nutrient solution at winter seasons from December to January. The average temperature of the nutrient solution was 12°C and the electric conductivity was 1.0 mS/cm. There is no heating treatment of the nutrient solution. Image processing techniques are used for measuring the leaf areas ratio on the lettuce plant growth. In the result, the lettuce plant growth treated by the high concentrated dissolved oxygen (23mg/l) is about 2.1 fold larger than that treated by the fully aeration of room air. Thus, it was found that the high concentrated dissolved oxygen (20-30 mg/l) supply was effective to improve the lettuce plant growth under a low greenhouse temperature in a deep hydroponic culture.