  We present Submillimeter Array observations of the massive star-forming
region IRAS 20126+4104 in the millimeter continuum and in several molecular
line transitions. With the SMA data, we have detected nine molecular
transitions, including DCN, CH3OH, H2CO, and HC3N molecules, and imaged each
molecular line. From the 1.3 mm continuum emission a compact millimeter source
is revealed, which is also associated with H2O, OH, and CH3OH masers. Using a
rotation temperature diagram (RTD), we derive that the rotational temperature
and the column density of CH3OH are 200 K and 3.7\times 1017 cm-2,
respectively. The calculated results and analysis further indicate that a hot
core coincides with IRAS 20126+4104. The position-velocity diagrams of H2CO
3(0,3)-2(0,2) and HC3N 25-24 clearly present Keplerian rotation. Moreover, H2CO
3(0,3)-2(0,2) is found to trace the disk rotation for the first time.
