Abstract: Automata theory is one of the foundations of theoretical computer science. Automata techniques have extensive use in many fields. Finite state automata are the recognizers of regular languages. Finite state automata have deterministic and nondeterministic models, which are equivalent with respect to the language recognizing ability. Weighted automata are finite automata with each transition associated besides an input symbol also an element from an algebraic structure. The weight of any input string can be computed. Any finite automaton is a special weighted automaton. So weighted automata are more powerful and have more applications.