  Isospin symmetry breaking in the quark condensates, $< \bar dd> \not= < \bar
uu>$, is a fundamental parameter in both the QCD sum rule studies and the
chiral perturbation theory. In this article, we apply the QCD sum rule method
to treat the hyperon mass difference ${1\over
2}(m_{\Sigma^-}+m_{\Sigma^0})-m_{\Sigma^+}$ in order to obtain a reasonable
estimate on such isospin symmetry breaking parameter $\gamma$ defined as $(<
\bar dd>-< \bar uu>)/ < \bar uu>$. Note that the electromagnetic contributions
to the particular mass difference are expected to cancel almost completely.
Using the light-quark mass difference $m_d-m_u=4\pm 1$ MeV and the experimental
data ${1\over 2}(m_{\Sigma^-}+m_{\Sigma^0})-m_{\Sigma^+}$$=5.62\pm 0.13$ MeV,
we obtain $\gamma= -0.011\pm 0.001$, a value which is slightly larger than the
commonly adopted value and is of smaller uncertainty.
