A dynamical system is an order pair (S, f) whereS is a semi group and f is a homomorphism fromS to S which is an endomorphism. In thisdynamical system (S, f) we introduced fixedpoints and periodic points and related resultsare obtained. Regular dynamical system andinversedynamical system is also defined andrelatedresults are obtained. In this paper it isimportant observe that regular element in asemi group is also a regular element in thedynamical system. Inverse dynamical system isintroduced and important results are obtained.