  We study the so-called magic mixing angles for doubly heavy baryons. Defining
that a magic mixing angle rotates states with definite $^{2S+1}(l_\lambda)_J$
to make them heavy-quark symmetric states, we derive the magic mixing angle
only in the case $L_\rho=0$ between the heavy quark symmetric states with
quantum numbers $\left(J, j_\ell\right)$ and the states with $\left(J,
s_q+j_\rho\right)=\left(J, \{^4l_\lambda/^2l_\lambda\}\right)$ for a doubly
heavy baryon in the standard $\rho-\lambda$ configuration, where $\vec
j_\ell=\vec l_\lambda+\vec s_q$, $\vec s_\rho=\vec s_{Q1}+\vec s_{Q2}$, and
$\vec j_\rho=\vec s_\rho+\vec L_\rho$. We discuss how this mixing angle affects
model building for a doubly heavy baryon.
