Using 5.3.0.Final, arbitrary facts and the rule shown below: import org.drools.reteoo.InitialFactImpl rule "Clear" when $f: Object() ####### then if( ! ($f instanceof InitialFactImpl) ){ System.out.println( "retract a " + $f.getClass() ); retract( $f ); } end This retracts my Foo, Bar and Counter facts. Good. $f: Object( class == Foo.class ) ####### changed This retracts all of my Foo facts. Excellent. $f: Object( class != Foo.class ) ####### changed again This retracts only Foo facts. Bad. -W