WIndows installer will see that it is not installed and won't run the command. So you don't have to check if it is installed.

Hi Martijn

Thanks for the reply.

If BDE is alredy uninstalled it will display the message "Are you sure want to uninstall this product? if i click ok buttom again one more message will dispaly i.e;  "This action is only valid for products that are currently installed."

How can i avoid this messages? How to uninstall it in quit mode?

Thanks.

With the latest version of Windows Installer it is prefered that you write out the options.
Completely silent: msiexec.exe /x{A7C849F7-64F1-4B5C-966B-4478EC6DFF89} /Quiet
Passive: msiexec.exe /x{A7C849F7-64F1-4B5C-966B-4478EC6DFF89} /Passive

If the uninstall wants to do a restart you can suppress that with the option REBOOT=ReallySuppress

>I am working on uinstall of BDE using registry key......

What do you mean by this?   Are you setting a run or runonce registry key to run this string during a boot or reboot?

I also note that you are asking if there is a condition to skip the uninstall if BDE is not installed. Does this mean you are trying to run MSIEXEC from within an existing MSI?  If you are, then you need to do this in the UI sequence or it will not work.

Finally, you could use System Search to look for a key file in the BDE install, and if it is found, then you will have set a public property ( eg  BDECHECK) with the path to the file. Then you simply use BDECHECK as the condition on your custom action. If BDE is present, BDECHECK will be "true" and your uninstall will run.