  We present 12CO (J=2-1) observations towards the central region of the
Seyfert 2 galaxy NGC 4258 with the Submillimeter Array (SMA). Our
interferometric maps show two arm-like elongated components along the major
axis of the galaxy, with no strong nuclear concentration. The CO (2-1)
morphology and kinematics are similar to previous CO (1-0) results. The
velocity field of the components agrees with the general galactic rotation,
except for the east elongated component, which shows a significant velocity
gradient along the east-west direction. In order to account for the velocity
field, we propose the kinematical model where the warped rotating disk is also
expanding. The line ratio of CO(2-1)/CO(1-0) reveals that the eastern component
with the anomalous velocity gradient appears to be warmer and denser. This is
consistent with the gas in this component being closer to the center, being
heated by the central activities, and possibly interacted by expanding motions
from the nuclear region.
