J2ME is the development platform for mobile devices with larger support and availability in the market right now. Due to the minimalist definition of this architecture it does include neither API's for data persistence management, like object serialization, and relational database access nor standard APIs to access a remote host. This paper presents J2MEMicroDB, an Open Source software that implements object serialization, a local relational database engine on the mobile device and a remote database access protocol that allows access to any JDBC database. In the design and implementation of J2MEMicroDB specific requirements and limitation of mobile devices have been considered. Even some performance improvements have been developed, like BTree indexing structures which improves significantly the efficiency of the searches, as the presented cross-platform benchmarking proves.