When compiling drls the kie maven plugin uses the plugin classpath instead of the project one. This imply that it is necessary to duplicate the dependencies used by the kie project also inside the plugin declaration, as reported by this email: http://drools.46999.n3.nabble.com/rules-users-Drool-6-0-0-Final-2-question-re-kie-maven-plugin-please-td4027117.html