The aim of study was to investigate the effect of CaO and SiO2 in controlling bacterial leaf blight disease on onion caused by Xanthomonas sp. in the net house and field conditions. In the net house conditions, the results showed that treatment mixture of CaO 0,97 g/kg of soil + SiO2 1,03 g/kg of soil was the most effective disease reduction, followed by mixture of CaO 0,72 g/kg of soil + SiO2 0,78 g/kg of soil, single CaO 0,97 g/kg of soil and SiO21,03 g/kg of soil. In the field experiment, the results showed that all treatments were effective in controlling the disease. In which, the treatment mixture of CaO 0,97 g/kg of soil + SiO2 1,03 g/kg of soil showed the highest efficacy in relieving the disease and stable during the survey. At the same time, this was also the treatment that resulted high commercial productivity and significant difference compared to the control treatment.