不变资本（德语：Konstantes Kapital；英语：Constant capital），是卡尔·马克思提出来的观念，指资本家购买生产资料的那部分资本。在生产过程中只是转移自身的价值量，不发生价值的增殖，由于其价值量不发生变化，所以叫做不变资本。

Constant capital (c), is a concept created by Karl Marx and used in Marxian political economy. It refers to one of the forms of capital invested in production, which contrasts with variable capital (v). The distinction between constant and variable refers to an aspect of the economic role of factors of production in creating a new value.