Background: Self-instructional module (SIM) on knowledge among staff nursesserves in order to prevent cardiothoracic post-operative complications Objectives: To assess the Effectiveness of self-instructional module (SIM) on knowledge regarding prevention of cardiothoracic post-operative complications among staff nurses working in selected hospital at Tumkur, Karnataka, India. Methods: The sample were divided in to group with pre-test and post-test pre experimental research design and all the relevant data were entered in a preformed format. Statistics: Percentage calculation was done to know the self-instructional module (SIM) on knowledge regarding prevention of cardiothoracic post-operative complications among staff nurses. In order to establish reliability, Test- Retest method and Karl Pearson’s correlation coefficient was computed from the scores and the obtained ‘r’ value was obtained. Results: In our study 90% belonged to age group of 20- 24 years and 10% to 25-30 years and none belongs to the age group of 36 years of age and above. Males were 90% and females were 10 %. In our study, 48% were general nurse and 52% were BSc nurses. Nurses serving in cardiothoracic intensive care unit were 58%, 32% were serving in surgical care unit, 10% were serving in intensive coronary care unit and none were serving in respiratory intensive care units. Clinical experiences constituted 84% having less than 3 years of experience, 12% had 3 - 6 years of experience and 4% had greater than 9 years of experience. Among the sample, 83% had exposure to training programme and 13% had exposure to television and 3% had exposure to newspaper. Knowledge level of the sample was 90% had below average knowledge, 10% had average knowledge, no one had above average knowledge on prevention of cardiothoracic post-operative complication in pre-test but in post-test no one had below average, 10% had average knowledge and 90% had above average knowledge on prevention of post-operative cardiothoracic complications. Conclusion: This shows that there is very high significance difference between the Knowledge levels of pre-test & post-test. By means of that we can conclude that the administered SIM on prevention of cardiothoracic post-operative complications was very effective. The implementation of self-instructional module improved the overall knowledge of Nurses regarding the prevention of cardiothoracic post-operative complications. Furthermore, knowledge has to improve in the areas like screening and prevention of post-operative cardiothoracic complications and there must be constant reinforcement to the staff nurses by conducting various continuing educational programmes.