Abstract: Objective To understand mental health status and its main influence factors among the medical staff working on the prevention of mother-to-child transmission of HIV in a high prevalence region of AIDS in Yunnan province.Methods Totally 255 medical staff selected from 13 counties in Yunnan province were investigated using Symptom Checklist 90(SCL-90) and a self-administered questionnaire.Results The total score and factor scores except interpersonal sensitivity were significantly higher in the medical staff than those of the national norm.The prevalence of psychological problem was 48.0%.The results of unconditional logistic regression analyses indicated that the risk factors for psychological problems were at age of 30-40 years,working with high frequency of direct contact to blood and body fluid,dissatisfaction with salary,unwillingness to deal with the job,without self-relief of work pressure,consideration of no adequate medical insurance for occupational exposure,and worry about unfriendly attitude of the patients and the protective factor was getting AIDS related training.Conclusion The psychological work pressure is great for the staff engaded in the prevention work on mother to-child transmission of HIV and is affected by many factors.Therefore,the implementation of integrated mental interference for the medical staff is necessary.