  KamLAND is a massive liquid-scintillator-based neutrino detector studying low
energy neutrino oscillation. The experiment has discovered a large deficit of
the reactor neutrino flux with baseline of 180km in the year 2002. This result
is placing a strong impact on the elementary particle physics. The KamLAND
detector makes use of one kiloton of liquid scintillator (LS) as the active
neutrino target. This is the largest homogeneous LS detector in the world.
Although the light yield and attenuation length of the LS were measured to be
57% anthracene and ~10m, in the test experiments, when it is used in the
KamLAND detector, the effective transparency and light yield significantly
increased from these values, presumably due to the scattering and re-emission
in the large scale LS. The radio active contamination in the LS is extremely
low, such as 3.5E-18g/g for uranium. This is the world's lowest contamination
record so far achieved and measured. The success of the KamLAND experiment is a
fruit of this high-quality and large-quantity LS. In this proceedings, an
outline of the LS is described.
