Student applicant’s cancellation often occurs in STMIK AMIKOM Yogyakarta. A student candidate, who has been succeeded in the admission test, cancels his/her application by disregarding the next phase of admission process (re-registration). This condition causes a detrimental effect for STMIK AMIKOM, this makes the number of new students always go under the desired capacity. If the possibility of the registration cancellation can be detected early, then the executive manager can make any attempts to keep the candidate go through the admission process and subsequently minimize the rate of admission cancellation. A research to detect the possibility of application withdrawal is carried out recalling a previous experience suitable for solving the current problem, the case search and matching process is made easier, an indexing method is conducted before forming a decision tree. The decision tree is developed using C4.5 algorithm, which is improvement from the predecessor ID3 algorithm. This application was designed to be flexible. It allows modifications of variables or training cases. As the trial medium, it used more than 1500 data records of new student applicants for 2006/2007 teaching season in STMIK AMIKOM Yogyakarta.