By sweeping the microwave frequency, we measured the Josephson plasma resonance for underdoped Bi:2212 and Bi:2201. The resonance enables us to determine the superfluid density and quasiparticle conductivity sigma(c)(qp) in the c axis accurately. In the slightly underdoped crystals, superfluid density shows very little change at low temperature, which is consistent with a d-wave coherent tunneling model. The c-axis superfluid response shows an unusual doping dependence, The T dependence of sigma(c)(qp) is very different from that in the ab plane. The Josephson coupling energy in single-layer Bi:2201 is a factor of 5000 smaller than predicted by the interlayer tunneling model.