  The \Sigma^0-\Lambda mixing angle in isospin-asymmetric nuclear medium is
investigated by using QCD sum rules. From the general consideration of the
in-medium baryonic correlations, in-medium baryon mixings are shown to have
several Lorentz structures such as the scalar mixing angle \theta^S and the
vector mixing angle \theta^V. This causes a difference between the particle
mixing \theta (= \theta^S + \theta^V) and the anti-particle mixing \bar{\theta}
(= \theta^S - \theta^V). From the finite energy sum rules for the
\Sigma^0-\Lambda mixing, we find that the in-medium part of the mixing angle
has a relation \theta^S_{Med} \simeq - \theta^V_{Med} in the isospin-asymmetric
medium. This implies that the medium affects mainly the anti-particle mixing.
  From the Borel sum rules, we obtain |\bar{\theta} - \theta_0| \simeq 0.39
|(\rho_n - \rho_p)| / \rho_0 with \theta_0, \rho_n, \rho_p and \rho_0 being the
vacuum mixing angle, the neutron density, the proton density and the normal
nuclear matter density respectively.
