Abstract: This study is about the Effectiveness of Internal Control System in the Private Banks of Trincomalee. There was found through observation and discussion that there are some deviations in the internal control system in the daily banking activities. Based on this problem the researcher was intended to do this research on the objectives of evaluate the bank’s control environment and internal control system in the bank, to identify the bank’s risk assessment process and the internal control in the bank, to evaluate bank’s accounting, information and communication system relevant to financial reporting and the internal control in the bank, to find out bank’s control activities affect the internal control in the bank and to find out bank’s self assessment affect the internal control in the bank. This study is based on the dependent variable; effective internal control and five independent variables; control environment, risk assessment,accounting,information and communication, control activities and self assessment.