在数学中，四次函数（英文：quartic function）表示形为(a≠0且a，b，c，d，e是常数)的多项式函数。

四次函数表达式的定义是一个四次多项式，因为x的最高次数是4。

如果令四次函数的值等于零，则可得一个四次方程。该方程的解称为方程的根或函数的零点。

This article is about the univariate quartic. For the bivariate quartic, see Quartic plane curve.

In algebra, a quartic function is a function of the form

where a is nonzero, which is defined by a polynomial of degree four, called quartic polynomial.

Sometimes the term biquadratic is used instead of quartic, but, usually, biquadratic function refers to a quadratic function of a square (or, equivalently, to the function defined by a quartic polynomial without terms of odd degree), having the form