美国护照最后一页写的是一个声明，内容如下：

"I, [护照持有人全名], hereby declare, on oath, that I absolutely and entirely renounce and abjure all allegiance and fidelity to any foreign prince, potentate, state, or sovereignty, of whom or which I have heretofore been a subject or citizen; that I will support and defend the Constitution and laws of the United States of America against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; and that I take this obligation freely, without any mental reservation or purpose of evasion; so help me God."

这段声明的大意是，护照持有人宣誓放弃对任何外国王子、统治者、国家或主权的忠诚和效忠，并承诺支持和维护美国宪法和法律，并为之忠诚和效忠。这是美国公民入籍时需要宣誓的内容，也是美国护照的最后一页必须写上的内容。这个声明的目的是确保美国公民在国际上的身份是单一的，并且忠诚于美国。