A one and a half year old baby crying at two o’clock in the middle of the night may be caused by physiological factors, but do not rule out pathological factors such as nutritional deficiencies, upper respiratory tract infections and so on. 1. physiological factors: such as the surrounding environment temperature is not comfortable, too loud, or the baby did not eat enough, want to urinate and defecate, etc., may cause a one and a half year old baby crying in the middle of the night at two o’clock. 2. Nutritional deficiencies: such as the baby is not often sunshine or failure to supplement the body’s need for nutrients in a timely manner, may lead to the baby’s lack of vitamin D or calcium deficiency, which leads to a one and a half year old baby crying in the middle of the night at two o’clock. 3. Upper respiratory tract infections: such as the presence of nasopharyngitis, laryngitis, etc., will lead to sleep breathing or throat discomfort, one and a half year old babies will cry to express their discomfort symptoms, leading to the emergence of the middle of the night two crying situation. One and a half year old baby crying in the middle of the night at two o’clock, may also be caused by other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, give targeted treatment or standardized treatment.