An American barrier option is an option contract in which the option holder receives an American option or becomes nullified conditional on the underlying stock price touching a barrier level. We use the Feynamn-Kac method to value American options and present analytic valuation formulas for American under the Black-Scholes pricing framework. Because the early exercise boundary of the American barrier option is different from the early exercise boundary of the vanilla American option, we claim the in-out parity does not hold.