Currently we are using Oracle9i Enterprise Edition Release 9.2.0.4.0 in sun solaris 5.9 server.

We wnt to upgrade the oracle database to 10.2g.

My doubt is that " what are the implications of this database upgradation in sun solaris server"

"whether we need to upgrade the sunsolaris 5.9 also"

Please help me in this regard.

depends on the patch level of your solaris installation... if you are on an up-2-date patchlevel there might be no impact. but you should read the oracle install notes really carefull!
for a detailed statement the information you provided isn't enough!

Some vendors like oracle have upgrade matrix that tell you what is or is not supported under which OS, the matrix will also tell you which product is going to be EOL.

The thing abt major upgrades is it's always fraught with uncertainty.

The main thing to worry abt is not the database or the OS, that's the least of your worries. The main thing is whether the application that uses the database will break after the upgrade especially if you are using unknown or customized 3rd party application software to access the database and some of these software may or may not work with higher OS.

Before you do any upgrade on the production you best first try it out in development then test if your apps and also your operation will still function after you upgraded the OS and database, don't take anything for granted.

Contacting Oracle support or their website www.meta~ is your best bet.