Salinity often increases osmotic stress, reducing plant water uptake and inhibiting the absorption of nutrients and minerals. This imbalance situation causes physiological, biochemical disorders, and nutrient deficiencies in plants. In this study, the effects of biochar application on the physiological properties, nutrient contents and antioxidant enzyme activities of lettuce were investigated under saline irrigation water conditions. For this purpose, four different biochar doses and different irrigation water salinity levels were applied to the lettuce plant. In the study, biochar application under salt stress conditions decreased the Na, Fe, Zn content and antioxidant enzyme activity of the plant. Leaf relative water content, chlorophyll content (SPAD) and some nutrients (Ca, K, Mg, P, Cu and Mn) also increased. Therefore, biochar applied under salt irrigated water conditions offers good potential to reduce the severity of plant exposure to salinity stress. In addition, the biochar amendment helped the plant uptake of nutrients.