For Oracle DBA Certification, you must have basic knowledge about Oracle Databases(whatever database is right now in working in ur country, i.e. 9i,10g,11g). After gathering knowledge on that,start preparing for the Oracle Certified Associate Certification(OCA).
After OCA, attain some work experience than go for OCP i.e. Oracle Certified Professional and than it is the big one Oracle Certified Master(OCM).
OCA is the entry level Certification. i prepared for it from books and study material from an e-learning site. Both the things helped specially the mock exams(practice test from Brain bench). I scored good marks n got promoted from junior team member to database manager of my team. i am preparing for OCP, professional level certification right now.
