Internal audit function is within an enterprise whose importance is extremely large in achieving the business excellence that is being sought. This paper presents internal audit as one of the three fundamental types of audit and its significance in the overall business process based on the identification and prevention of possible irregularities in the work and presentation of data in the financial statements. The basis for quality implementation of the internal audit process lies in the good planning of the internal audit project itself and the implemented internal control system. Without adequate control the company will not be able to achieve its goals. Internal audit is therefore one of the best control tools a company can have because it is included as part of the company in all business processes and more easily identifies weaknesses of a company. The planning process and the internal auditing program in this paper are presented in the example of the selected company.