体内平衡（homeostatic，又称恒定状态或恒定性）是指在一定外部环境范围内，生物体或生态系统内环境有赖整体的器官的协调联系，得以维持体系内环境相对不变的状态，保持动态平衡的这种特性。

器官与器官之间必须经由调整和监管机制保持平衡，才能使整个基体的正常运作。在人类，体内平衡包括以下的内容：

Homeostasis or homoeostasis is the property of a system in which variables are regulated so that internal conditions remain stable and relatively constant. Examples of homeostasis include the regulation of temperature and the balance between acidity and alkalinity (pH). Human homeostasis is the process that maintains the stability of the human body's internal environment in response to changes in external conditions.