Non-invasive monitoring performed by breath analysis to achieve early diagnosis of diabetic ketosis have at tracted widespread attention. In this study, mixed potential type acetone sensors based on Ce_0.8Gd_0.2O_1.95solid electrolyte and Bi1−xLaxFeO₃(x = 0.1, 0.3, 0.5, 0.7, 0.9) sensing electrode (SE) were fabricated successfully and used for the diagnosis of diabetic ketosis through analyzing the concentration of acetone in expiration. The sensor attached with Bi_0.5La_0.5FeO₃-SE presented the highest sensitivity towards acetone among other sensors fabricated in this work, which could detect 1 ppm acetone with the response value of −3 mV. Meanwhile, this sensor showed a relatively high sensitivity of −17.5 mV/decade towards 1–5 ppm acetone at 580 °C. The sensor also displayed excellent repeatability, good selectivity, humidity stability and acceptable long-term stability during 30 days continuously working at 580 °C. Based on the sensing performance of this sensor, the exhalation of diabetics were measured, and results indicated that the sensor used Bi_0.5La_0.5FeO₃-SE exhibited stable and reliable characteristics to the breath tests of diabetics. In addition, a positive correlation relationship between acetone concentration in the exhalation of ketosis patients and the blood ketone level were obtained, and this relationship was consistent with reports from other literatures. Hence, in terms of breath detection, this sensor has the potential to detect diabetic ketosis.