Background: Genetic amniocentesis (AC) is a method of prenatal diagnosis (PND) for fetal chromosomal abnormalities and method for prevention and control of genetic diereses. Pregnant women who do not understand this method will have anxiety and may be refuse the procedures. The preparatory information probably reduce the anxiety and increase the acceptance of AC clients. Objective: To study the result of the preparatory information in anxiety level, knowledge and attitudes of AC clients Study designs: Randomized controlled trial Setting: Outpatient department, Srinagarind hospital, faculty of Medicine, Khon Kaen University. Methods: The study included 70 pregnant women who had undergone AD from January to October 1997 and randomly assigned into control (35 cases) and study group (35 cases). Measurement: The AC clients (both control and study groups) was requested to compldete questionnaires before and after procedures. The completed questionnaires were examined by microcomputer (SPSS/pc+ program) and analysed using analysis of covariance and t-test Results: The AC clients who received the preparatory information (study group) had less anxiety level, more knowledge and better attitudes than control group significantly (P<0.05). Conclusions: The study showed that the preparatory information could reduce the anxiety level, increase knowledge and make positive attitudes of the AC clients. Therefore, the preparatory information should be available and essential part of PND service in every centers.