Our system is currently running in a BizTalk 2009 and its databases is created in SQL 2005 instance.
We are planning to upgrade our BizTalk to 2010 by still using the same databases. Is it possible to use the same databases that was created in a SQL 2005 instance and restore it to a SQL 2008 instance to configure the BizTalk 2010, since BizTalk 2010 does not support SQL 2005?
While you can upgrade BizTalk Server and SQL Server, this is generally not the preferred approach. If you can, the better plan would be to stage a new BizTalk Server Group and migrate all the applications.
Note, the current version of BizTalk Server is 2013 R2. BizTalk Server 2010 is no longer available.
If you must upgrade, the BizTalk databases will be upgraded with BizTalk Server. You can them upgrade SQL Sever or move the databases to the new SQL Server. But this is still not the best way.