Objective: Search the optimal treatment for infantile lactose intolerance. Methods: Separate 360 infants who are diagnosed as infantile lactose intolerance into outpatient treatment group (hereinafter referred to the outpatient group, n = 309 ) and inpatient treatment group ( referred to as the inpatient group, n = 51 ). The outpatient group is given a short term lactose-free formula feeding, i.e. stop breast milk in first 1-2 days and use lactose-free formula feeding, from the 2nd-3rd day, gradually increase the feeding frequency and quantity depending on the defecation situation. The transition time lasts for 3 to 7 days, and then the breast milk feeding is restored. This method is named the ecological treatment method, because it conform to the laws of nature: removal of lactose in milk, no drugs. The inpatient group is given a routine examination, cephalosporins ( 50 ~ 100 ) mg / kg-1 for inflammation, montmorillonite powder for diarrheal and Bifidobacterium tablets for intestinal flora disturbance . During hospitalization, for those who have respiratory complications, the antibiotic is adjusted, the management of respiratory is strengthen and simultaneously the Cough and phlegm medicine treatment is given; for those who have pseudomembranous colitis, the antibiotic is immediately stopped, and is replaced by an oral metronidazole ( 20 ~ 30 ) mg / kg-1 and supplement of water and electrolyte and nutrition support are given. Results: The average turnaround time for symptoms of diarrhea: Outpatient group ( 2.74 + 1.575) d, inpatient group ( 14.30 + 11.597) d. There is a significant difference ( t = 0.00749, P < 0.01 ) between the two groups; The pseudomembranous colitis during the treatment: Outpatient group has 0 case (0% ), inpatient group has 3 cases (0.45%). There is a significant difference (u =1.6528, P＜0.05) between the two groups; Respiratory infection: Outpatient group has 38 cases ( 12.298 ) %, inpatient group has 16 cases (31.373 ) %. There is a sig