Two ways:

1. Go to the plugins directory of your Eclipse installation, e.g.
e:\eclipse\plugins, and look for a folder whose name starts
"org.apache.ant". The last part of the name of that folder indicates the
version of Ant you are using, e.g. org.apache.ant_1.6.5 indicates that you
are using Ant 1.6.5.

2. Right-click on any build file, e.g. build.xml. Choose "Run as -> Ant
Build...". Choose the "Main" tab. Enter this in the "Arguments:" text
area: -version. Click the Apply button. Click the Run button. The build file
will run and display the Ant version, the current date, and the elapsed time
to run the build file. The actual targets and tasks in the build file will
not be executed. (Naturally, you should remove '-version' from the Arguments
portion of the Main tab after you have determined what version of Ant you
are running; otherwise, you will only ever get the Ant version when you run
that build file.)

--
Rhino