  We study the quark-gluon mixed condensate g<\bar{q} sigma G q>, using the
SU(3)c lattice QCD with the Kogut-Susskind fermion at the quenched level. We
generate 100 gauge configurations on the 16^4 lattice with \beta = 6.0, and
perform the measurement of the mixed condensate at 16 points in each gauge
configuration for each current quark mass of m_q=21, 36, 52 MeV. Using the 1600
data for each m_q, we find the ratio between the mixed condensate and the quark
condensate, m_0^2 = g<\bar{q} sigma G q> / <\bar{q}q> \simeq 2.5 GeV^2 at the
lattice scale of 1/a \simeq 2 GeV in the chiral limit. The large value of the
mixed condensate suggests its importance in the operator product expansions in
QCD. We study also chiral restoration at finite temperature in terms of the
mixed condensate, which is another chiral order parameter. We present the
lattice QCD results of the mixed condensate at finite temperature.
