  We present \sim1" resolution 1.3 millimeter dust continuum and spectral line
(12CO and 13CO J=2-1) observations of the transitional disk system HD 135344B
obtained with the Submillimeter Array. The disk shows a Keplerian rotation
pattern with an inclination of \sim11{\deg}, based on the spatially and
spectrally resolved 12CO and 13CO emission. The data show clear evidence for
both dust and gas surface density reductions in the inner region of the disk
(radius \lesssim 50 AU) from the continuum and 13CO J=2-1 data, respectively.
The presence of this inner cavity in both the dust and gas is more consistent
with clearing by giant planet formation than by photoevaporation or by grain
growth. There is also an indication of global CO gas depletion in the disk, as
the mass estimated from 13CO emission (\sim3.8 \times 10^(-4) M\odot) is about
two orders of magnitude lower than that derived from the 1.3 mm continuum
(\sim2.8 \times 10^(-2) M\odot).
