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Abstract Background and objectives: Acquired immune deficiency syndrome(AIDS) is one of the most well-known disease in the world .It is not only A heaththrapeutic problem but also with politic ,social, cultural and economic aspects. Paying attention to high-risk groups such as Lab staff is important. we decided to study and compare the knowledge of public and private Laboratories staff. Material and Methods: This cross sectional study, descriptive-analytic,was conducted on 350 personnel of private laboratories and educational centers of Shiraz University of Medical Sciences,2011.We collected Information by using a questionnaire including three parts of demographic characteristic questions, questions about knowledge in different fields of AIDS and those related to the performance of personnel. The results were reported as tables and graphs and analyzed by ANOVA,t-test and square. Results: The data, in different areas of AIDS, in public and private laboratories are similar and the difference statistically is not significant. Regarding to symptoms and treatment, the knowledge of privale Lab staff is higher than stste ones and this difference is significant (P=0.01).As a whole,the results show the knowledge of staff about the transmission modes(92.7%),the pathologic agent(99.2%),at risk people (61.2%)and preventive measure (53.1%).both group have good practice in wearing gloves and using disposable syringes.Regarding to disposing infectious waste material,private and state center practice are 92.6% and 77%,respectively. Conclusion: Based on the result,the knowledge relating to preventive procedures and at risk people of AIDS is not enough.Thereforeit is a necessity to hold in service training for Lab staff,stressing on disposing infectious waste materials. Key words: AIDS, laboratory personnel, knowledge, practice