  Quasars are essential for astrometric in the sense that they are spatial
stationary because of their large distance from the Sun. The European Space
Agency (ESA) space astrometric satellite Gaia is scanning the whole sky with
unprecedented accuracy up to a few muas level. However, Gaia's two fields of
view observations strategy may introduce a parallax bias in the Gaia catalog.
Since it presents no significant parallax, quasar is perfect nature object to
detect such bias. More importantly, quasars can be used to construct a
Celestial Reference Frame in the optical wavelengths in Gaia mission. In this
paper, we compile the most reliable quasars existing in literatures. The final
compilation (designated as Known Quasars Catalog for Gaia mission, KQCG)
contains 1843850 objects, among of them, 797632 objects are found in Gaia DR1
after cross-identifications. This catalog will be very useful in Gaia mission.
