  We present the results of first dual-beam observations with VERA (VLBI
Exploration of Radio Astrometry). The first dual-beam observations of a pair of
H2O maser sources W49N and OH43.8-0.1 have been carried out on 2002 May 29 and
July 23, and fringes of H2O maser lines at 22 GHz have been successfully
detected. While the residual fringe phases of both sources show rapid
variations over 360 degree due to the atmospheric fluctuation, the differential
phase between the two sources remains constant for 1 hour with r.m.s. of 8
degree, demonstrating that the atmospheric phase fluctuation is removed
effectively by the dual-beam phase referencing. The analysis based on Allan
standard deviation reveals that the differential phase is mostly dominated by
white phase noise, and the coherence function calculated from the differential
phase shows that after phase referencing the fringe visibility can be
integrated for arbitrarily long time. These results demonstrate VERA's high
capability of phase referencing, indicating that VERA is a promising tool for
phase referencing VLBI astrometry at 10 microarcsec level accuracy.
