SAP Business One is a SAP product that uses ERP-based solutions for MSMEs. Even though SAP Business One has supported many business processes that exist in SMEs, not all business processes have been supported by SAP Business One, therefore additional solutions that are integrated with SAP Business One are often required. In this research, an add-on solution will be added in the form of a .NET based web and android application to support the stock taking process. Therefore, it requires data integration between SAP Business One and the add-on application that has been made. In data integration research between SAP Business One with web and android applications will be carried out with the Accelerated Implementation Program (AIP) methodology, which is the methodology issued by SAP for the implementation or customization of SAP Business One. The tool used is the SAP Business One SDK with a User defined Field (UDF). The Android application will retrieve data from SAP Business One then after being processed by Android the data will be given to the web application via API access carried out by Android, after that the web application will provide data on the SAP Business One application. With the integration of add-on and SAP Business One applications using User-defined Fields, MSMEs can easily add applications that are capable of supporting MSME business processes that are not supported by SAP Business One. Keywords: ERP, ERP UMKM, SAP Business One, Android, Web .NET, SAP Business One SDK, Accelerated Implementation Program.