Java 2 Micro Edition (J2ME) technology has been designed to bring a common framework of development for mobile devices. This can bring the Java development approach of "develop once run everywhere" to the Mobile application emerging market. Combined with the widespread of the support for this platform among the park of mobile devices, all of this makes J2ME a suitable option for mobile application development.

However, J2ME has been designed to run in small devices, that?s why the APIs (Application Programming Interface) implemented are very limited and kept to the strictly necessary. This decision has let out all the structured data persistence management, like object serialization, and the relational database access; neither to store data inside the mobile device nor to access a remote host.

This paper presents J2MEMicroDB, an Open Source development that implements Object Serialization, local relational database engine and a remote database access protocol that allows the 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, as the cross-platform presented benchmarking proves.