Objective: The aim of this investigation was to evaluate the effect of preoperative education on postoperative anxiety and pain in breast cancer patients. Material and Methods: The sample of this semi-experimental study was consisted of 60 (30 were, 30 were control group) modified radical mastectomy patients who admitted a university hospital's general surgery department between August 2005 and February 2006. The data were collected from the demographic questionnaire, the state and trait anxiety inventory, visual analog scale and analgesia observation form. The control group did not have any intervention other than routine care, and they completed the state anxiety inventory scale approximately 24 hours before the operation. As in control group, the study group completed the state anxiety inventory scale and they were given a preoperative education program which assisted by an education booklet. In the study and control groups; state anxiety levels, pain levels, blood pressures and pulse rate were measured for 48 hours after the operation with regular intervals. Results: There was not any significant difference between the study and the control groups in terms of preoperative state and trait anxiety levels (p>0.05). Postoperative state anxiety scores in the control group were found as 52.70 +/- 5.78 while, the anxiety scores were 34.53 +/- 3.79 in the study group. There were statically significant differences in trait anxiety scores between the groups (p<0.05). When the postoperative pain status of the patients was considered, the difference in visual analog scale scores of the two groups was found to be significantly different (p<0.01). In comparison of control and patient groups, the differences between the postoperative blood pressure and the heart rate were not statistically significant at all measurement points (p>0.05). Conclusion: It is found that informative and educative nursing approach has a significant effect on reducing postoperative anxiety and pain.