This paper presents for the first time, the use of a microfluidic channel with organic substrates to reduce the size of different antenna designs at 915 MHz (dipole and loop). The channel was created by drilling a cavity on a 50 mil RO3003™ substrate and bonding it to two 5 mil substrates in order to seal the structure. Compared to designs fabricated on an unperturbed substrate, the overall size reduction in length for the dipole with water-filled channel was ∼44% (60 mm), while a 54% reduction in area was observed for its loop counterpart. Broad bandwidths of 22% and 11% were achieved for the water loaded dipole and loop, respectively. The results obtained for both designs agreed well with simulations.