  We report measurements of radiative B decays with K eta gamma final states,
using a data sample of 140 /fb recorded at the Upsilon(4S) resonance with the
Belle detector at the KEKB e+e- asymmetric energy collider. We observe B -> K
eta gamma for the first time with a branching fraction of (6.9 +1.7-1.6 (stat)
+1.3-1.0 (syst)) X 10^{-6} for M(Keta) < 2.4 GeV/c2. We also set an upper limit
on B -> K3*(1780) gamma.
