We present a channel drop filter by using channel drop tunneling processes in a two-dimensional triangular lattice photonic crystal slab. The channel drop filter is composed of two waveguides and two donor-type three-missing-holes cavities. At resonance, the power transferred to the drop waveguide and the power remaining in the bus are found to be about 61% and 5%, respectively. In order to improve the filter response, the out-of-plane quality factor must be much higher than the in-plane quality factor. (C) 2004 Elsevier B.V. All rights reserved.