  In this note we prove the backwards uniqueness of the mean curvature flow for
(codimension one) hypersurfaces in a Euclidean space. More precisely, let $F_t,
\widetilde{F}_t:M^n \rightarrow \mathbb{R}^{n+1}$ be two complete solutions of
the mean curvature flow on $M^n \times [0,T]$ with bounded second fundamental
forms. Suppose $F_T=\widetilde{F}_T$, then $F_t=\widetilde{F}_t$ on $M^n \times
[0,T]$. This is an analog of a result of Kotschwar on the Ricci flow.
