My apologies for not being more specific. The version of drools is 4.07 and the size is of the serialized file. It is 2megs. We do not currently have about 200 rules. Cheers, Blair Message: 2 Date: Fri, 20 Feb 2009 22:16:40 +0000 From: Mark Proctor <mproctor(a)codehaus.org&gt; Subject: Re: [rules-users] Large Rule base failing? StackOverlowError To: Rules Users List <rules-users(a)lists.jboss.org&gt; Message-ID: <499F2BC8.5050708(a)codehaus.org&gt; Content-Type: text/plain; charset="iso-8859-1" Christie, Blair wrote: What version of Drools? You have 2 million rules? Just to be clear, was it working with 1.9 million rules? heh I'm intigued on what sort of app you are doing, could you do a write up? I'm sure people would love to know about people using a really large number of rules. The limitation you reaching is a limitation of the standard serialisation algorithm of the JDK, we would have to create a custom marshaller to improve this further, which we may do in the future. Unless someone from the community wants to do this? :) Mark ------------------------------------------------------------------------