When I should rebuild the index in oracle database?

You should not rebuild indexes based on a schedule.

Rather You will/can rebuild an index in response to Identified and
Degraded performance (on a period). It is the RARE index that needs to be rebuilt.



See more....
https://forums.oracle.com/forums/thread.jspa?threadID=626809&start=0&tstart=0
https://forums.oracle.com/forums/thread.jspa?messageID=2017174&
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:6601312252730
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:2913600659112
http://richardfoote.files.wordpress.com/2007/12/index-internals-rebuilding-the-truth.pdf
http://www.jlcomp.demon.co.uk/index_efficiency.html
http://www.jlcomp.demon.co.uk/index_efficiency_2.html
http://jonathanlewis.wordpress.com/index-efficiency-3/
http://jonathanlewis.wordpress.com/2008/09/26/index-analysis
http://www.orafaq.com/wiki/Oracle_database_Performance_Tuning_FAQ#When_should_one_rebuild_an_index.3F
http://webcache.googleusercontent.com/search?q=cache:80JD78CDuH0J:www.dba-oracle.com/art_index1.htm+When+I+should+rebuild+the+index+in+oracle+database%3F&cd=1&hl=en&ct=clnk
https://blogs.oracle.com/sysdba/entry/when_to_rebuild_index