  The uncertainty in the calculation of atmospheric neutrino fluxes is studied.
The absolute value of atmospheric neutrino fluxes is sensitive to variation of
the primary cosmic ray flux model and/or the interaction model. However, the
ratios between different kind of neutrinos stay almost unchanged with these
variations. It is unlikely that the anomalous ratio
$(\nu_{\mu}/\nu_e)_{obs}/(\nu_{\mu}/\nu_e)_{MC}$ reported by Kamiokande and
Super Kamiokande is caused by the uncertainty of predicted atmospheric neutrino
fluxes.
