This study is about The Implementation of I-Pos Application in Business Process at Delivery Department of PT Pos Indonesia (Persero) MPC (Mail Processing Centre) Semarang. The objective of the study, first is to find out the business process of post mail service especially at Delivery Department of MPC Semarang, second is to find out the operation of I-Pos Application at Delivery Department, the last is to find out the constraints, problems and it’s solution when using the I-Pos Application. The methods of data collection were done by interview, observation, and literature study. Data collected was presented in descriptive writing. The study shows that the business process of post mail service began with receiving mails from other Department, sorting mails based on delivery areas of delivery officer, entry DO, sorting mails based on delivery address, delivery process and update status. The constraints were found that access to local database had to experience a delay process and the connection to the national database was sometimes disrupted. The solution from the first problem could only be done by IT officer, whereas second problem could be resolved by coordination of IT officer with Head Office’s I-Pos Team for checking network. Based on the data collected, it can be concluded that the implementation of I-Pos Application at Delivery Department strongly related with I-Pos applications used in other department such as Post Mail Department and Post International Department. Therefore, there are two modules of I-Pos Application used in Delivery Department; namely “Bukti Serah” Application and Delivery Application. Delivery Application is used by delivery officers who are obligated to sort and update the status of their post mails, while Bukti Serah Application is used for accepting the mails from other department so that the mails were allowed to be processed by Delivery Department.