  We calculate the decay rate B-> X_s photon photon via intermediate
psuedoscalar charmonium eta_c. This process is thought to be the main
long-distance contribution which dominates the corresponding inclusive rare B
decay. We point out that once the momentum dependence of eta_c-> photon photon
conversion strength, due to off-shellness of the intermediate eta_c, is taken
into account, the rate of this decay mode is reduced. The change in
differential decay rate in region of spectrum immediately below m_{eta_c} is
more significant. On the other hand, we point out that the unexpectedly large
branching ratio for B-> X_s eta' which is recently observed by CLEO could
indicate a potentially larger long-distance contribution via eta' resonance.
