  We propose a scheme to initiate and examine Rayleigh-Taylor instability in
the two species Bose-Einstein condensates. We identify $^{85}$Rb-$^{87}$Rb
mixture as an excellent candidate to observe it experimentally. The instability
is initiated by tuning the $^{85}$Rb-$^{85}$Rb interaction through magnetic
Feshbach resonance. We show that the observable signature of the instability is
the damping of the radial oscillation. This would perhaps be one of the best
controlled experiments on Rayleigh-Taylor instability. We also propose a semi
analytic scheme to determinate stationary state of binary condensates with the
Thomas-Fermi approximation for the axis symmetric traps.
