Regular expressions are very meaningful and now-a-days broadly used to represent signatures of various attacks. The focal component of today's security systems like intrusion detection and prevention system is a signature based regular expression matching. Deterministic finite automaton is often used to represent regular expressions. In regular expression matching, storage space of Deterministic finite automata is very important concern. A massive amount of memory is essential to store transition function of Deterministic finite automata. The method described in this paper reduces size of Deterministic finite automata which is in regular expression format. The performance of the regular expression matching by compressing Deterministic finite automata is evaluated by using regular expression set. General TermsPattern matching algorithms, Network Security, Theory of Computations. KeywordsRegular expressions; security attacks; deterministic finite automata; intrusion detection and prevention.