  We prove the non-degeneracy for the critical Lane--Emden system $$ -\Delta U
= V^p,\quad -\Delta V = U^q,\quad U, V > 0 \quad \text{in } \mathbb{R}^N $$ for
all $N \ge 3$ and $p,q > 0$ such that $\frac{1}{p+1} + \frac{1}{q+1} =
\frac{N-2}{N}$. We show that all solutions to the linearized system around a
ground state must arise from the symmetries of the critical Lane-Emden system
provided that they belong to the corresponding energy space or they decay to 0
uniformly as the point tends to infinity.
