一次得救永远得救（Once saved, always saved，简称OSAS）亦称圣徒的坚忍（Perseverance of the saints）、圣徒蒙保守（Preservation of the Saints）或永远的保障（Eternal Security），是源于基督教的神学理论之一，指如果一个人相信耶稣基督得救以后，他便可永远得救。

基督教神学家加尔文（1509－1564年）从新旧约经文的注解与整理时，侧重上帝的主权与其工作，由此带出上帝对其选民的保守，而选民在保守中得以有力量来实践信仰。其后，加尔文的追随者在相关神学议题的论辩中，便归纳出此说，属「五点加尔文主义」（Five-Point Calvinism）之一。

Perseverance of the saints (also referred to as eternal security as well as the corollary—though distinct—doctrine known as "Once Saved, Always Saved") is a teaching that asserts that once persons are truly "born of God" or "regenerated" by the indwelling of the Holy Spirit, nothing in heaven or earth "shall be able to separate (them) from the love of God" (Romans 8:39) resulting in a reversal of the converted condition.