  We study the scenario where a sneutrino is the next lightest supersymmetric
particle (NLSP) and decays into a gravitino and standard model particles. The
daughter particles such as neutrinos and quarks cause electro- and hadronic
showers and affect big-bang nucleosynthesis. It is found that despite a small
branching ratio, four-body processes including quarks in the final state give
the most stringent constraint on the sneutrino abundance for gravitino mass of
1 $-$ 100 GeV. Pion production by high energy neutrinos is important when the
sneutrinos decay at $\sim$ 1 sec. We also discuss the thermal leptogenesis in
the sneutrino NLSP scenario.
