在线性代数及相关数学领域中，零矢量（也称退化矢量）即欧几里得空间里的中所有元素都为 0 的矢量 (0, 0, …, 0)。零矢量通常记为、0 或 0。

在一般的矢量空间中，零矢量是唯一确定的矢量。它是矢量加法的单比特。

证明：零矢量是唯一的：若 a 和 b 为零矢量，则 a = a + b = b。

In mathematics, given a vector space X with an associated quadratic form q, written (X, q), a null vector or isotropic vector is an element x of X for which q(x) = 0.

In the theory of real bilinear forms, definite quadratic forms and isotropic quadratic forms are distinct. They are distinguished in that only for the latter there exists a nonzero null vector. Where such a vector exists, (X, q) is called a pseudo-Euclidean space.